Carbon dioxide separation using adsorption with steam regeneration

ABSTRACT

A process for separating a carbon dioxide from a gas stream is disclosed. The process can include passing the gas stream over a sorbent that adsorbs the carbon dioxide by concentration swing adsorption and adsorptive displacement. The sorbent can be regenerated and the carbon dioxide recaptured by desorbing the carbon dioxide from the sorbent using concentration swing adsorption and desorptive displacement. A carbon dioxide separation system is also disclosed. Neither the system nor the process rely on temperature swing or pressure swing adsorption.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application, filed Jul. 8, 2014, under 35 U.S.C. §119(e), claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/843,736,filed Jul. 8, 2013, entitled “Carbon Dioxide Separation Using Adsorptionwith Steam Regeneration,” the entire contents and substance of which arehereby incorporated by reference as if fully set forth below.

STATEMENT OF FEDERALLY SPONSORED RESEARCH

Portions of this disclosure were made with Government support underGrant Number DE-NT0005497, awarded by The Department of Energy. TheGovernment may have certain rights in the disclosure.

TECHNICAL FIELD

The various embodiments of the disclosure relate generally to processes,methods, and systems for the separation of CO₂ from mixed gas streamsusing an essentially isothermal cyclic adsorption process. It isparticularly useful for CO₂ capture from combustion gases and can beused for other applications such as natural gas purification forexample.

BACKGROUND

Fossil fuels currently supply the majority of the world's energy needsand their combustion is the largest source of anthropogenic carbondioxide emissions. Carbon dioxide is a greenhouse gas and is believed tocontribute to global climate change. Concern over global climate warminghas led to interest in capturing CO₂ emissions from the combustion offossil fuels. CO₂ can be removed from combustion flue gas streams byvarying methods.

Combustion gases vary in composition depending on the fuel and theconditions of combustion. The combustion gases can be produced infurnaces and in gas turbines, including the combustion gases produced inthe generation of electric power. The fuels used are predominantly coaland natural gas. Coal is burned in furnaces, while natural gas is burnedboth in furnaces and in gas turbines, but in electric power generationnatural gas is mainly burned in gas turbines.

The quantities of combustion gas produced in electric power generationare very large because of the scale of furnaces and turbines used. Onemeasure of the scale of these operations is the amount of CO₂ producedin a typical 500 Megawatt power plant. For coal fired power generation,the rate of CO₂ production is on the order of 100 kilograms per second;for gas fired power production it is more like 50 kilograms per second.

The challenge for flue gas CO₂ capture is to do it efficiently tominimize the cost. All post-combustion CO₂ capture technologies sufferfrom the disadvantage that the CO₂ in the flue gas is present at lowpressure (just about 1 atm) and in low concentrations (3 to 15%). Alarge amount of energy is needed to separate the CO₂. For 90% recoveryof 10% CO₂ in a flue gas at 1 atm, the CO₂ must be brought from 0.1 atmto 1 atm, and then further compressed to a delivery pressure of 150 atm.Analyses conducted at NETL shows that CO₂ capture and compression usinga conventional absorption process raises the cost of electricity from anewly built supercritical PC power plant by 86%, from 64 cents/kWh to118.8 cents/kWh (Julianne M. Klara, DOE/NETL-2007/1281, Revision 1,August 2007, Exhibit 4-48 LCOE for PC Cases). Aqueous amines areconsidered a state-of-the-art technology for CO₂ capture for PC powerplants, but have a cost of $68/ton of CO₂ avoided) (Klara 2007,DOE/NETL-2007/1282). Developing methods that minimize the amount ofenergy and other costs will be necessary if CO₂ removal from flue gas isto be economical.

Methods for the removal of CO₂ from gas streams, include adsorption witha solvent, adsorption with a sorbent, membrane separation, and cryogenicfractionation and combinations thereof. In absorption/adsorptionprocesses to capture CO₂, the energy needed to regenerate the sorbent orsolvent is a large cost element.

The heat of adsorption is generally lower than the heat of absorption.This could make use of physical adsorbent for CO₂ capture attractivebecause it has a lower energy requirement for the desorption reaction torelease the CO₂. A physical adsorbent can be used for CO₂ capture. Usingmolecular sieves/zeolites and activated carbon, this approach for CO₂capture has been research by Inui 1988 [Inui, T., Okugawa, Y. andYasuda, M. (1988), Relationship between properties of various zeolitesand their CO2 adsorption behaviours in pressure swing adsorptionoperation, Industrial & Engineering Chemistry Research, 27, 1103], Chue1995 [Chue, K. T., Kim, J. N., Yoo, Y. J., Cho, S. H. and Yang, R. T.(1995), Comparison of activated carbon and zeolite 13× for CO2 recoveryfrom flue gas by pressure swing adsorption, Industrial & EngineeringChemistry Research, 34 (2), 591-598], Siriwrdane 2001 [Siriwardane, R.V., Shen, M., Fisher, E., and Poston, J. A., (2001) “Adsorption of CO₂on Molecular Sieves and Activated Carbon,” Energy and Fuels, Vol. 15,pp. 279-284, 2001], Siriwrdane 2005a [Siriwardane, R. V., (2005a) “SolidSorbents for Removal of Carbon Dioxide from Low Temperature GasStreams”, U.S. Pat. No. 6,908,497 B1, Jun. 21, 2005], Siriwrdane 2005b[Siriwardane, R. V., Shen, M., and Fisher, E., (2005b) “Adsorption ofCO₂ on Zeolites at Moderate Temperatures,” Energy and Fuels, Vol. 19 No.3, p. 1153, 2005], Muñoz et al (2006) [Muñoz, Emilio, Eva Díaz, SalvadorOrdóñez, and Aurelio Vega “Adsorption of Carbon Dioxide on Alkali MetalExchanged Zeolites”], Gingichasvili (2008) [Gingichashvili Sarah (May19,2008)—http://thefutureofthings.com/news/1183/co2-absorption-made-easier.html],Halmann and Steinberg (1999) [Halmann, M M and M Steinberg, (1999)Greenhouse Gas—Carbon Dioxide Mitigation: Science and Technology. LewisPublishers, Boca Raton, Fla.] and Lee (2005) [Lee, Sunggyu (2005)Encyclopedia of Chemical Processing Vol 1. CRC Press].

Many physical adsorbent separation systems use pressure swing absorption(PSA) for regeneration. PSA can be used to regenerate CO₂ adsorbents. Itis used in environmental control applications to maintain CO₂ level (Lee2005 [Lee, Sunggyu (2005) Encyclopedia of Chemical Processing Vol 1. CRCPress]) Also, PSA is used for removal of CO₂ down to very low levels ingas purification (U.S. Pat. No. 5,656,064). Applying PSA to atmosphericflue gas separation would have high energy consumption requirements (duethe requirement to pull a hard vacuum when removing CO₂ from a flue gas)and capital costs because of the large pressure ratios required toenable complete desorption of the CO₂.

Temperature swing absorption is another well-established regenerationmethod. This has been applied to adsorbent regeneration by Lee (2005)[Lee, Sunggyu (2005) Encyclopedia of Chemical Processing Vol 1. CRCPress].

Such separation processes are also commonly applied for CO₂ separationsof gases from non combustion gas streams, e.g. natural gas purification,re-breathers, contained environment CO₂ concentration control andothers.

BRIEF SUMMARY

The various embodiments of the disclosure relate generally to processes,methods, and systems for adsorbing CO₂ from a gas stream on a sorbent,and regenerating the sorbent by desorbing the CO₂.

An embodiment of the disclosure can be a process for separating CO₂ froma gas stream, including the steps of passing a gas streaming comprisingCO₂ over a sorbent to adsorb the CO₂ to the sorbent, and recovering theCO₂ by desorbing the CO₂ from the sorbent. The process does not includepressure swing adsorption and temperature swing adsorption. The processcan include adsorption of CO₂ by concentration swing adsorption andadsorptive displacement, and can include desorption of the CO₂ from thesorbent with by a combination of concentration swing desorption anddesorption displacement. The process can include treating the sorbentwith steam to displace the CO₂ from the sorbent.

The process can be conducted at a constant pressure, and atapproximately isothermal conditions. The adsorption of CO₂ step candecrease the temperature of the sorbent during adsorption. In anembodiment, the temperature decreases during step a) by no more thanabout 20° C. The desorption step can increase the temperature of thesorbent during desorption. In an embodiment, the temperature increasesby no more than about 20° C.

In the process, the sorbent can include an alkalized substrate,including an alkalized alumina.

An embodiment of the disclosure can also be a sorbent based CO₂adsorption process, which includes the steps of preparing a sorbentcomprising an alkalized substrate, passing a gas stream containing CO₂across the sorbent to adsorb the CO₂ onto the alkalized substrate, andrecovering the CO₂ from the sorbent by passing steam across the CO₂containing alkalized substrate to displace the CO₂ with water. Theprocess does not include pressure swing adsorption or temperature swingadsorption. The adsorption process can include concentration swingadsorption and adsorptive displacement of the CO₂ onto the sorbent, andthe desorption process can include recovering the CO₂ by a combinationof concentration swing desorption and desorptive displacement.

In an embodiment, the alkalized substrate can include a substrate and atleast one alkali or alkaline earth component, or the alkalized substratecan include an alumina component and at least one alkali or alkalineearth component, or the alkalized substrate which consists essentiallyof an alumina component and at least one alkali or alkaline earthcomponent.

An embodiment of the invention can be a CO₂ separation system, whichincludes a CO₂ adsorption zone; a CO₂ desorption zone; one or more CO₂sorbent beds, and a CO₂ feed stream. The sorbent bed can alternatebetween the adsorption zone and the desorption zone, adsorb CO₂ from theCO₂ feed stream in the adsorption zone and desorb CO₂ in the desorptionzone. The system does not include pressure swing or a temperature swingadsorption.

The system can also include an inlet and an outlet for the adsorptionzone where the CO₂ feed stream enters the adsorption zone via the inletand a purified feed stream exits the adsorption zone via the outlet. Thesystem can also include an inlet and an outlet for the desorption zone,wherein a stream comprising steam enters the desorption zone via theinlet and a CO₂ enriched stream exits via the outlet. The system canfurther include a purge stage after the desorption zone, wherein thesorbent bed enters the purge stage and is purged via a stripping gasstream.

The adsorption zone in the system can operate as concentration swing andadsorptive displacement, and the desorption zone can operate asconcentration swing and desorptive displacement. The adsorption zone canhave an adsorption inlet and an adsorption outlet, the desorption zonehave a desorption inlet and a desorption outlet, and the adsorptioninlet and adsorption outlet can be in opposing positions from thedesorption inlet and the desorption outlet, relative to the sorbent bed.

The system can include at least two sorbent beds, and the at least twosorbent beds can rotate through each of the adsorption and desorptionzones. At least two sorbent beds can include two or more sorbent beds,three or more sorbent beds, four or more sorbent beds, five or moresorbent beds, or six or more sorbent beds. In an embodiment, the sorbentbeds can be a plurality of sorbent beds rotating in series through theadsorption zone, desorption zone, and optionally though a purge stageafter the desorption zone and/or optionally through a purge stage afterthe adsorption zone.

Another embodiment of the disclosure is a method for purifying a CO₂ gasstream to increase the concentration of the CO₂ in a product streamwhich includes the steps of preparing a sorbent bed having an inlet andan outlet, passing a gas stream containing CO₂ across the sorbent bed toadsorb the CO₂ to the sorbent, recovering a CO₂-enriched stream bypassing steam across the CO₂ containing sorbent. The method does notinclude a pressure swing adsorption or temperature swing adsorptionprocess.

The adsorption can be by a concentration swing adsorption and adsorptivedisplacement. The CO₂ can be recovered by a combination of concentrationswing desorption and desorptive displacement. The method can recovergreater than 80% by volume of the CO₂ from the feed stream into theCO₂-enriched stream or greater than 85% by volume of the CO₂ into theCO₂-enriched stream.

Another embodiment of the disclosure is a method for removing CO₂ topurify a gas stream, including the steps of preparing a sorbent bedhaving an inlet and an outlet, passing a gas stream containing CO₂across the sorbent bed from inlet to outlet to adsorb the CO₂ to thesorbent, recovering the purified gas stream depleted of CO₂ at theoutlet, and regenerating the sorbent bed by passing steam across the CO₂containing sorbent. The method does not include a pressure swingadsorption or temperature swing adsorption process. The method canreduce the amount of CO₂ in the purified gas stream by at least 80% byvolume, by at least 85% by volume, or by at least 90% by volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a graphical representation of a cyclic displacementprocess in accordance with an exemplary embodiment of the disclosure.

FIG. 2 illustrates a representation of a CO₂ separation system inaccordance with an exemplary embodiment of the disclosure.

FIGS. 3A through 3F illustrate a five-bed simulated moving bed systemand associated valve positions, in accordance with an exemplaryembodiment of the disclosure.

FIGS. 4A through 4F illustrate another five-bed simulated moving bedsystem and associated valve positions, in accordance with an exemplaryembodiment of the disclosure.

FIGS. 5A and 5B illustrate an eight-bed simulated moving bed system, inaccordance with an exemplary embodiment of the disclosure.

FIG. 6 illustrates a simulated moving bed system, in accordance with anexemplary embodiment of the disclosure.

FIG. 7 illustrates a counter-flow moving bed design, in accordance withan exemplary embodiment of the disclosure.

FIG. 8 illustrates another moving bed design, in accordance with anexemplary embodiment of the disclosure.

FIG. 9 illustrates a stacked moving bed design with a bucket elevator,in accordance with an exemplary embodiment of the disclosure.

FIG. 10 illustrates a counter-flow rotary wheel bed design, inaccordance with an exemplary embodiment of the disclosure.

FIG. 11 illustrates the external housing and structure of the rotarywheel design of FIG. 12, in accordance with an exemplary embodiment ofthe disclosure.

FIG. 12 illustrates a nonlimiting twenty four sorbent cell rotary wheeldesign, along the A-A line of FIG. 11, in accordance with an exemplaryembodiment of the disclosure.

FIG. 13 illustrates the transition zone between adsorption andregeneration in the rotary wheel of FIG. 12, in accordance with anexemplary embodiment of the disclosure.

FIG. 14 illustrates interior vertical cross-section of the rotary wheelof FIG. 12, along the B-B line, in accordance with an exemplaryembodiment of the disclosure.

FIG. 15 illustrates a sorbent cell rotary wheel design, in accordancewith an exemplary embodiment of the disclosure.

FIG. 16 illustrates another sorbent cell rotary wheel design, inaccordance with an exemplary embodiment of the disclosure.

FIG. 17 illustrates another sorbent cell rotary wheel design, inaccordance with an exemplary embodiment of the disclosure

FIGS. 18A and 18B illustrate an individual sorbent module and interbedspacers or flow channels, in accordance with an exemplary embodiment ofthe disclosure.

FIGS. 19A and 19B illustrate an inlet-outlet view and sideview of alayered beds system, in accordance with an exemplary embodiment of thedisclosure.

FIG. 20 illustrates a segmented sorbent bed in accordance with anexemplary embodiment of the disclosure.

FIG. 21 illustrates a representation of a cyclic displacement process,in accordance with an exemplary embodiment of the disclosure.

FIG. 22 illustrates a multiple fixed bed test apparatus for continuousCO₂ capture, in accordance with an exemplary embodiment of thedisclosure.

FIG. 23 illustrates inlet and outlet gas composition for a sorbent bed,in accordance with an exemplary embodiment of the disclosure.

FIG. 24 illustrates the percent CO₂ from regeneration of the sorbent bedof FIG. 22, in accordance with an exemplary embodiment of thedisclosure.

FIG. 25 illustrates inlet and outlet gas composition for another sorbentbed, in accordance with an exemplary embodiment of the disclosure.

FIG. 26 illustrates a graphical display of results in a cyclicdisplacement system, in accordance with an exemplary embodiment of thedisclosure

FIGS. 27 and 28 illustrate the effect of water on CO₂ adsorption for twosorbents, in accordance with an exemplary embodiment of the disclosure.

FIGS. 29A and 29B illustrate the CO₂ loading of several sorbents, inaccordance with an exemplary embodiment of the disclosure.

FIG. 30 illustrates an 8-bed simulated moving bed apparatus, inaccordance with an exemplary embodiment of the disclosure.

FIGS. 31-33 illustrate gas flow results for a series of sorbents, inaccordance with exemplary embodiments of the disclosure.

FIGS. 34A-34D illustrate a multiple bed simulated moving bed apparatusincluding optional recycle streams, in accordance with exemplaryembodiments of the disclosure.

FIGS. 35A-35D illustrate a multiple bed simulated moving bed apparatusincluding optional steam saver, in accordance with exemplary embodimentsof the disclosure.

DETAILED DESCRIPTION

Although preferred embodiments of the disclosure are explained indetail, it is to be understood that other embodiments are contemplated.Accordingly, it is not intended that the disclosure is limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Thedisclosure is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the preferredembodiments, specific terminology will be resorted to for the sake ofclarity.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise.

Also, in describing the preferred embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

Ranges can be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment includes fromthe one particular value and/or to the other particular value.

By “comprising” or “comprising” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in adevice or system does not preclude the presence of additional componentsor intervening components between those components expressly identified.

A sorbent-based process to separate carbon dioxide (CO₂) from a gasstream is disclosed. The sorbent can have alkali or alkaline earthelements dispersed on a solid. Examples of solids that can be usedinclude alumina, carbon, resin, silica, other oxides or admixtures. Theprocess employs gas-solids contactors in which the sorbent isalternately exposed to the feed gas and to steam wherein the gas andsteam are essentially at the same temperature. In the steaming step thecarbon dioxide adsorbed from the gas is released from the sorbent by acombination of concentration swing and desorptive displacement, therebyregenerating the sorbent for re-use. No external application or removalof heat is used, and the process operates at essentially constantpressure. The process is notably identifiable and distinguishable andbeneficial as compared to pressure swing or partial pressure swingseparation in that during the adsorption of CO₂ the bed temperaturedecreases below the average bed temperature as determined over theentire cycle and during CO₂ displacement/desorption the bed temperatureincreases above the average. The process is further distinguished andbeneficial as compared to thermal swing separation in that no externalheat is applied and the desorption gas, steam, is essentially isothermalwith the feed gas. The gas-solids contactors may use moving solidsorbents, or solid sorbents contained in packed beds or inparallel-channel beds (monoliths). The packed bed or monoliths can berotating or stationary. The water and energy from the regeneration steamcan be recaptured after use and recycled back into the process.

The disclosure provides for a process for adsorbing and desorbing CO₂.The process can be notably identifiable and distinguishable andbeneficial as compared to pressure swing or partial pressure swingseparation in that, during the adsorption of CO₂, the bed temperaturedecreases below the average bed temperature as determined over theentire cycle and, during CO₂ displacement/desorption, the bedtemperature increases above the average. The process can be furtheridentifiable and distinguishable and beneficial as compared to thermalswing separation in that no external heat is applied and the desorptiongas, steam, can be essentially isothermal with the feed gas. Thegas-solids contactors can use moving solid sorbents or solid sorbentscontained in packed beds or in parallel-channel beds (monoliths). Thepacked bed or monoliths can be rotating or stationary. To permitcontinuous flow of inlet and outlet streams, multiple beds can becombined with appropriate valving to switch individual beds betweenadsorption and desorption. Such multiple bed arrangements can beoperated to achieve counter-current staging. The water and energy fromthe regeneration steam can be recaptured after use and recycled backinto the process. The process can be operated at temperatures greaterthan 100° C. enabling, for example CO₂ removal from flue gases exiting aheat recovery steam generator (HRSG) without extensive heating orcooling.

The disclosure further provides a regeneration process which usescontact with steam to remove the adsorbed gas from the sorbent. Theregeneration mechanism can be by a combination of concentration swingand desorptive displacement of the adsorbed gas with steam. Thedisclosure can further relate to a method to recycle the steam andrecover its energy through a multi-stage condenser/heat exchangerssystem. The advantage of this option is that it increases systemefficiency.

The disclosure also relates to gas separations such as removal of CO₂from a combustion flue gas or natural gas stream or other streams. Thedisclosure further provides a process for selecting and/or making aregenerable sorbent for CO₂ capture. This solid sorbent can adsorb CO₂.An advantage is that the adsorbent can be rapidly regeneratedessentially isothermally with steam and discharge a moist CO₂ streamwherein the CO₂ concentration is higher than that in the original feedgas. Another advantage of the sorbent is that it can be used in anadiabatic reactor design. The sorbent adsorbs water during regenerationwith steam and then desorbs water during CO₂ adsorption so that the netreactions are exothermic during steaming and endothermic duringadsorption. In this way the system does not require external thermalmanagement on the adsorber and regenerator beds. This modest temperatureswing is also important because it thermally assists both adsorption anddesorption, again without the addition of external thermal management.

High process efficiency can be important in order for CO₂ capture to beeconomical. The regeneration system can be designed to recycle the steamand recover its energy.

The advantages can include the following: (1) no pressure or temperatureswing is required; (2) effective for low CO₂ content gas; (3)achievement of low pressure drop with packed bed can be obtained withreduced footprint stacked fixed beds; (4) optional separation of bedvoid gases from adsorbed species during regeneration; (5) applicable toa variety of feeds; (6) does not require cooling of sorbent afterregeneration prior to adsorption; (7) applicable to feed gastemperatures >100° C.; (8) moist CO₂ discharge from the regenerationcycle can be at concentration greater than the feed CO₂ concentration;(9) option to utilize combustion air before going to combustion deviceas an additional stripping gas; (10) optional selective purging andrecycle to optimize the recovery and purity and energy efficiency.

The process can be carried out in a cyclic adsorption/regeneration cycleand can include various intermediate purges and stream recycles. Such aprocess can be performed with co-directional flow of the feed gas andregeneration steam, but can be preferably performed with counter-currentfeed adsorption/steam regeneration steam flows.

In an embodiment, the disclosure can include a process for separatingCO₂ from a gas stream. In general, the process can include the steps ofpassing a gas stream comprising CO₂ over a sorbent to adsorb the CO₂ tothe sorbent, and then recovering the CO₂ by desorbing the CO₂ from thesorbent. As noted above, and discussed in more detail below, theadsorption/desorption process can be based on concentration swing anddesorptive displacement. Concentration swing adsorption (CSA) processesincluding the adsorption and desorption steps are governed by change infugacity of the adsorbate, in this case, CO₂, in the gas stream, incomparison to the adsorbent. The adsorbate, in this case CO₂, isadsorbed when its fugacity is high in the gas stream and low in theadsorbent. Conversely, it is desorbed when its fugacity is reduced inthe gas stream relative to the amount in the adsorbent. By way ofexample, an adsorbent having a high level of CO₂ might still adsorbadditional CO₂ when the gas stream has a relatively higher fugacity ofCO₂ versus the adsorbent. And an adsorbent having a low level of CO₂ canadsorb CO₂ when the gas stream has a low fugacity of CO₂ so long as therelative fugacity of CO₂ in the sorbent is still lower than the CO₂ inthe gas stream. One of ordinary skill in the art would also recognizethat “relative fugacity” does not imply relative concentration in theabsolute value sense, i.e. does not mean that a 2% adsorbed CO₂ contentis necessarily larger than a 1% CO₂ gas level, because the ability ofthe gas to retain CO₂ versus the ability of adsorbent to adsorbadditional CO₂ will be governed by various equilibrium relationships.

The disclosure includes the process of desorbing the CO₂ from thesorbent. This step might also be referred to as a regeneration stepbecause the sorbent is regenerated for the next passage of a CO₂ gasstream across the sorbent. The desorption of CO₂ from the sorbentcomprises treating the sorbent with steam. This desorption step can bedriven by a one or more forces. One desorption force is concentrationswing, as with the adsorption step above. The partial pressure of CO₂ inthe incoming steam is nearly zero, and thus the adsorbed CO₂ can shiftto the steam phase. The second desorption force is desorption bydisplacement. The water molecules in the steam can adsorb onto thesorbent and displace the CO₂ from the sorbent.

As an optional step, the processes, methods and systems of thedisclosure can also include one or more purging step, in which anon-adsorbent gas, i.e. not steam or a CO₂ feed stream, can be passedacross the sorbent. The gas can be any gas known to one or ordinaryskill in the art, such as for example an inert gas or air. In anembodiment, the purge gas can be a nitrogen stream, an air stream, or adry air stream. Alternatively the purge gas can be a CO₂ feed gas orsteam that is recycled into a process step. The purge step can beconducted at any time. For example, prior to the passing of the CO₂ feedstream across the sorbent, a purge gas can be passed to remove residualand adsorbed water vapor. This purge gas can be run back into theregeneration side in order for the water vapor to be readsorbed onto theregeneration side. The purging step can also occur between theadsorption step or steps, and the desorption or regeneration step orsteps. The purge gas can be non-reactive, but can still optionallyremove adsorbed CO₂ from a sorbent based on concentration swing. Thus,in an embodiment, the purging step can be conducted after adsorptionsteps, and can be conducted to remove residual gas prior to desorption,which can be optionally recycled into the process. Moreover, the purgestep can also be optionally diverted into two streams: 1) an initialpurge stream to remove the first gas, and 2) a separate purge streamthat can contain the initial purified or desorbed CO₂, which could beoptionally captured as part of the final product stream. Furthermore, inan embodiment, a purging step can be conducted after the desorption orregeneration step(s) is complete, thereby optionally removing residualwater and/or steam which can be recycled back into the process. Eachpurging step can thereby reduce an excess gas stream which can, forexample lead to a more efficient process or produce a more CO₂ enrichedproduct stream because a final product stream is not diluted by apreceding gas source. By way of specific example, a purging stepconducted after the initial adsorption can remove residual, dilute CO₂feed stream, leading to a more concentrated CO₂ product stream. Theresulting gas stream from the purging step can be recycled into thesystem, or split into a recycle and a product stream.

In contrast to numerous processes currently applied to CO₂ processing,the processes, methods and systems of the disclosure do not includeeither pressure swing adsorption or temperature swing adsorption. Theprocess, method, and systems are nearly isothermal, i.e. there issubstantially no temperature change in the overall system. One ofordinary skill would understand that substantially no temperaturechange, or nearly isothermal, means that the overall temperature of thesystem does not change by a significant amount. That does notnecessarily mean that the temperature is perfectly fixed. Any system cangain or lose heat due to a number of factors, e.g. environmentalfactors, process fluctuations, etc. However, the disclosed process doesnot have a temperature change of more than 10° C. in either direction,more than 5° C. in either direction, or more than 3° C., or 2° C., or 1°C. in either direction.

While the overall process can be nearly isothermal, the individual stepsof adsorption and desorption steps can include independent temperaturechanges. In an embodiment, the adsorption process can result in atemperature decrease in the adsorption step. The adsorption of the CO₂on a sorbent can be an endothermic process that results in a temperaturedecrease in the system. Thus, in an embodiment, the temperature of thegas stream during adsorption can decrease by about 30° C. or less, byabout 25° C. or less, by about 20° C. or less, about 15° C. or less,about 10° C. or less, or about 5° or less. The temperature of the gasstream during adsorption can decrease by about 1° or more. On the otherhand, the desorption process can result in a temperature increase forthe desorption step. The desorption can be a net exothermic process thatresults in a temperature increase. Thus, in an embodiment, thetemperature of the gas stream during desorption can increase by about30° C. or less, by about 25° C. or less, by about 20° C. or less, about15° C. or less, about 10° C. or less, or about 5° or less. Thetemperature of the gas stream during desorption can increase by 1° C. ormore. However, as discussed, the input and outputs of the overall systemresult in a process that can be overall nearly isothermal.

Because the process does not rely on a temperature swing adsorption, theprocess can be conducted at any temperature in which the gas flows canbe maintained across the adsorbent. The process can often include acombustion gas stream and steam as a regeneration stream, so the overalltemperature of the process, method, or system can be conducted atgreater than about 100° C., greater than about 110° C., greater thanabout 120° C., greater than about 130° C., greater than about 140° C.,greater than about 150° C., or greater than about 160° C. The overalltemperature of the process can also be conducted at a temperature ashigh as the sorbent can withstand. Thus, the overall temperature of theprocess can be up to about 300° C., can be up to about 275° C., can beup to about 250° C., can be up to about 240° C., can be up to about 230°C., can be up to about 220° C., can be up to about 210° C., or can be upto about 200° C. However, the process can also be conducted at atemperature below 100° C., at conditions that allow the flow of steam ina gas stream, i.e. according to conditions known to one of ordinaryskill as derived from engineering Steam Tables. In an embodiment, theprocess can be conducted at a temperature between about 120° C. to about250° C., 120° C. to about 220° C., between about 120° C. to about 200°C., between about 140° C. to about 250° C., between about 140° C. toabout 230° C., or between about 140° C. to about 220° C. In anembodiment, the process can be conducted at a temperature between about120° C. to about 180° C., between about 140° C. to about 160° C., orbetween about 150° C. to about 165° C.

The process, method, and systems of the disclosure are also conducted ata nearly constant pressure, or a substantially constant pressure, i.e.there is substantially no pressure change designed as part of theprocess or system. Again, one of ordinary skill would understand thatsubstantially no pressure change means that the overall pressure of thesystem does not change by a significant amount. That does notnecessarily mean that the pressure is perfectly fixed. Any system cangain or lose pressure due to a number of factors, e.g. environmentalfactors, process fluctuations, etc. Because the process does not rely onpressure swing adsorption, the process, method, or system can be run atany pressure convenient to one of ordinary skill in the art. In anembodiment, the process, method, or system can be conducted at ambientpressure. However, one of ordinary skill in the art would also recognizethat gases in general, and steam in particular, can be modified based onchanges in temperature and pressure. For example, the system could berun below 100° C. with steam by running at a slightly reduced pressure.Similarly, higher temperature steam and gas can be used at ambientpressure, but might also be used at higher pressures. However, thepressure of the system overall, whether below, above, or at ambientpressure, does not vary significantly during the process.

As noted above, a driving force for adsorption anddesorption/regeneration of the CO₂ can be a combination of concentrationswing and desorptive displacement/adsorption. During adsorption,incoming CO₂ molecules adsorb onto the sorbent and also displacepreviously adsorbed water (adsorptive displacement or displacementadsorption), during which time the water also desorbs by concentrationswing. During desorption/regeneration, the water molecules from thesteam adsorb onto the adsorbent and displace the CO₂ (desorptivedisplacement or displacement desorption). Thus, there are severalmechanisms occurring during adsorption and desorption. The CO₂ in thefeed stream adsorbs onto the sorbent and also displaces water in theadsorption portion of the cycle, herein defined as the portion of thecycle where CO₂ containing gas is fed to the sorbent, and the sorbentadsorbs CO₂ and desorbs water. The CO₂ then desorbs during steamregeneration portion of the cycle, when the sorbent adsorbs water anddisplaces CO₂. Further steaming can further remove CO₂ from the sorbentvia continued displacement and partial pressure purge desorption. Theadsorbed water is then partially or completely displaced and partialpressure desorbed during the next CO₂ adsorption cycle. Two displacementreactions that are part of the overall adsorption/desorption process canbe defined: adsorptive displacement, in which an incoming CO₂ displaceswater from the sorbent during an adsorption step; and desorptivedisplacement, in which an adsorbed CO₂ molecule is displaced from thesorbent by steam during the desorption/regeneration step. These mightalso be called displacement adsorption and displacement desorption.

A non-limiting example of the type of reaction involved in adsorptionand desorption can be described in the following equations. While thenon-limiting example given is specific for a particular potassiumcarbonate hydrate, many related alkali and alkaline-earth carbonatehydrates may exhibit similar related adsorption and desorptionmechanisms. Under low water content conditions in adsorption portion ofthe cycle:2K₂CO_(3*)3H₂O+2CO₂

4KHCO₃+H₂Osupport*H₂O

support+H₂OUnder high water content, e.g. steam, conditions in regeneration portionof the cycle:4KHCO₃+H₂O

2K₂CO_(3*)3H₂O+2CO₂support+H₂O

support*H₂OAlternatively, the adsorption/desorption mechanism can be simplycompetitive adsorption between CO₂ and H₂O on basic sites wherein underhigh water vapor conditions the competitive adsorption favors water overCO₂.

The adsorption and desorption of H₂O on the non-alkali sites isgenerally not beneficial to the process efficiency. While the adsorptionof water on the non-alkali/alkaline sites may serve to help produce ahigher concentration moist CO₂ discharge stream, generally it serves toconsume steam in a non-productive manner, shifting it to the adsorptioneffluent. Thus, the preferred sorbent for this disclosure is one whichminimizes this part of the adsorption mechanism.

The disclosure can also include a sorbent based CO₂ adsorption processthat includes the steps of passing a gas stream containing CO₂ acrossthe sorbent to adsorb the CO₂ onto the alkalized substrate, andrecovering the CO₂ from the sorbent by passing steam across the CO₂containing alkalized substrate to displace the CO₂ with water. Theprocess can include also preparing a sorbent comprising an alkalizedsubstrate for the sorbent based CO₂ adsorption process. As discussedabove, the sorbent based CO₂ adsorption process does not includepressure swing adsorption or temperature swing adsorption. Theadsorption of CO₂ includes concentration swing adsorption of the CO₂onto the sorbent and adsorptive displacement, and the desorption andrecovery of the CO₂ can include a combination of concentration swingdesorption and desorptive displacement.

The processes and methods of the disclosure can also include a methodfor purifying a gas stream that contains CO₂ in order to reduce the CO₂in the gas stream. The method for removing CO₂ to purify a gas streamcan include preparing a sorbent bed having an inlet and an outlet,passing a gas stream containing CO₂ across the sorbent bed from inlet tooutlet to adsorb the CO₂ to the sorbent, recovering the purified gasstream depleted of CO₂ at the outlet, and regenerating the sorbent bedby passing steam across the CO₂ containing sorbent. The method does notinclude a pressure swing adsorption or temperature swing adsorptionprocess, and uses concentration swing adsorption and adsorptivedisplacement to remove the CO₂ during adsorption.

Similarly, the processes and methods of the disclosure can also includea method for purifying a CO₂ gas stream to increase the concentration ofthe CO₂ in a product stream. The method can include the steps ofpreparing a sorbent bed having an inlet and an outlet, passing a gasstream containing CO₂ across the sorbent bed to adsorb the CO₂ to thesorbent, and recovering a purified CO₂ stream by passing steam acrossthe CO₂ containing sorbent to generate an enriched CO₂ stream.

The adsorption and desorption processes, methods and systems of thedisclosure can be highly effective at capturing and recovering CO₂ froma stream. In an embodiment of the disclosure, the processes and methodscan recover greater than about 60% by volume of the CO₂ from theincoming gas stream, greater than about 65% by volume of the CO₂ fromthe incoming gas stream, greater than about 70% by volume of the CO₂from the incoming gas stream, greater than about 75% by volume of theCO₂ from the incoming gas stream, greater than about 80% by volume ofthe CO₂ from the incoming gas stream, greater than about 85% by volumeof the CO₂ from the incoming gas stream, greater than about 90% byvolume of the CO₂ from the incoming gas stream, or greater than about95% by volume of the CO₂ from the incoming gas stream. By analogy then,the initial stream fed across the sorbent during the adsorption phasecan be purified of at least about 60% volume of the initial CO₂, atleast about 65% volume of the initial CO₂, at least about 70% volume ofthe initial CO₂, at least about 75% volume of the initial CO₂, at leastabout 80% volume of the initial CO₂, at least about 85% volume of theinitial CO₂, or at least about 90% by volume or greater than about 95%by volume of the CO₂ in the feed stream. In an embodiment, the feedstream can be purified by less than 99.5% by volume.

As a complement to the reduction of CO₂ in the incoming gas stream, i.e.the CO₂ feed stream, the amount of CO₂ capacity of the sorbent can alsobe described. The ability of a sorbent to adsorb larger amounts of CO₂in an individual adsorption step leads to a direct increase inthroughput, due to overall capacity. The CO₂ loading of a sorbent can bedescribed by the percent weight increase of the sorbent due to increasedamounts of CO₂, based on, for example, the amount of CO₂ extracted froma feed gas versus the total weight of the sorbent. One of ordinary skillwould understand that several factors can affect the CO₂ capacity in agiven sorbent, including for example the temperature of the system, therelative basicity of the sorbent based on the amount of alkali oralkaline earth component on a given sorbent, and so forth. In anembodiment, a sorbent can have a CO₂ loading of at least about 0.4 wt %,at least about 0.5 wt %, at least about 0.6 wt %, at least about 0.7 wt%, or at least about 0.8 wt %. In an embodiment, the CO₂ loading can beat least about 1.0 wt %, at least about 1.2 wt %, at least about 1.3 wt%, at least about 1.4 wt %, at least about 1.5 wt %, at least about 1.6wt %, at least about 1.7 wt %, at least about 1.8 wt %, or at leastabout 1.9 wt %. In an embodiment, the CO₂ loading of a sorbent can be atleast about 2 wt %, at least about 2.5 wt %, or at least about 3 wt %.In an embodiment, the sorbent can have a CO₂ loading of less than 20 wt%. The CO₂ loading or capacity of a sorbent can be measured by anytechnique known to one of ordinary skill, including for example a TGAanalysis, or process evaluation to calculate the amount of CO₂ extractedfrom a feed gas per amount of sorbent.

The capacity of a sorbent bed, the concentration of CO₂ in the feedsteam, and other process parameters such as bed volume and air velocitycan be used to determine the overall cycle time of a given step for anadsorption or desorption bed. In an embodiment, the cycle time anabsorption or desorption bed can be from about 20 seconds to about 30minutes, including about 20 seconds to about 300 second, about 30seconds to about 150 seconds, about 1 minute to about 10 minutes, about1 minute to about 8 minutes, about 1 minute to about 5 minutes, about 1minute to about 15 minutes, about 1 minute to about 20 minutes, about 1minute to about 30 minutes, about 3 minute to about 30 minutes, about 5minute to about 30 minutes, about 5 minute to about 20 minutes, or about5 minute to about 15 minutes.

The adsorption step of the disclosure is also relatively insensitive tomoisture. The CO₂ feed streams can often contain water. For examplecombustion gas can contain 8-15 percent water. Other traditionalsorbents such as cationic zeolites are almost completely incapable ofadsorbing CO₂ in the presence of water. In comparison, the currentadsorption process can be conducted in the presence of water withoutsubstantial attenuation of the working capacity for CO₂. Thus, in anembodiment of the disclosure, the adsorption step can be conducted at apercent water volume of up to about 35 vol %, up to about 30 vol %, upto about 28 vol %, up to about 25 vol %, up to about 23 vol %, or up toabout 20 vol %. In an embodiment, the ratio of water to CO₂ in the feedstream can be greater than 0.5:1, greater than 0.75:1, greater than 1:1,greater than 1.5:1, greater than 2:1, greater than 2.5:1 or greater than3:1. In an embodiment, the ratio of water to CO₂ in the feed stream canbe less than about 4:1, less than about 3.5:1, less than about 3:1, lessthan about 2.5:1, or less than about 2:1.

The processes, methods, and systems of the disclosure can be used toadsorb CO₂ from a feed stream having a large range of CO₂concentrations. In an embodiment, the CO₂ concentration of the feedstream can be at least about 0.5 vol %, at least about 1 vol %, at leastabout 1.5 vol %, at least about 2 vol %, at least about 2.5 vol %, atleast about 3 vol %, at least about 4 vol %, or at least about 5 vol %.The CO₂ concentration can be at least about 6 vol %, at least about 7vol %, at least about 8 vol %, at least about 9 vol %, or at least about10 vol %. In an embodiment, the CO₂ concentration in the feed stream canbe less than about 50 vol %, less than about 45 vol %, less than about40 vol %, less than about 35 vol %, or less than about 30 vol %. Theprocesses, methods, and disclosures can be particularly effective atthese lower concentrations. However, the system can also be used toextract CO₂ at concentrations above 50 vol % as well, including up toabout 100%.

As discussed above, the process, method, and systems of the disclosureare conducted on a sorbent. The term sorbent can sometimes be appliedinterchangeably within this disclosure with the term adsorbent, and canbe sometimes described as the gas-solids contactor. The sorbent of thedisclosure can be an alkalized substrate or support, sometimes analkalized alumina.

The desirable characteristics of sorbents for use in this process caninclude adsorption capacity for CO₂ in the presence of water vapor, highselectivity for CO₂ adsorption versus other (non-water) components inthe feed gas, low steam requirement for regeneration, long-term physicalstability and adsorption capacity maintenance, low cost per unit weight,and good mass transfer characteristics. The desirable characteristicscan be obtained with various supported alkali and or alkaline-earthspecies.

Sorbents for this disclosure comprise alkali or alkaline earth metals,oxides, hydroxides, carbonates, bicarbonates or hydrates of any of thosespecies supported on a high surface area substrate. The high surfacearea substrate can be aluminas, silica-aluminas, carbon, pillared clays,silicas, resins, titanias and other water-stable supports. In anembodiment, the high surface area substrate or support can be alumina.In an embodiment, the sorbents can consist essentially of alkali oralkaline earth metals, oxides, hydroxides, carbonates, bicarbonates orhydrates of any of those species supported on a high surface areasubstrate; or can consist of alkali or alkaline earth metals, oxides,hydroxides, carbonates, bicarbonates or hydrates of any of those speciessupported on a high surface area substrate.

Alkali metals are elements in the left-most column of the periodic tableof chemical elements except that hydrogen is not included. Li, Na, K,Rb, Cs, and Fr are generally recognized as alkali-metals. Alkaline-earthmetals are in the second column from the left on the periodic table ofelements and are Be, Mg, Ca, Sr, Ba, Ra. The basic adsorbent in thisprocess can be an alkalized alumina. Alkalized alumina contains at leastone alkali or one alkaline component and at least one alumina component.The alkali or alkaline component can be in the pure state or as acompound, e.g. carbonate, hydroxide, oxide, etc. In some cases thealkali or alkaline compound can be in the form of hydrates. The alkalior alkaline surface can attract the acidic CO₂.

Any support upon which reasonable dispersion of the alkali metal speciescan be obtained can be useful, including resins, titania, zirconia,aluminas, silicas, clays, mixed inorganics and other inorganic andorganic support materials with significant surface areas upon which thealkali metal species can be reasonably dispersed. When the high surfacearea substrate or support is alumina, the alumina compounds can includesodium aluminate (2NaAlO₂═Na₂O*Al₂O₃), gamma (γ)-Alumina {Al₂O₃(G)},theta (θ)-alumina, hydrated alumina (Boehmite, Al₂O₃*H₂O), Gibbsite,Bauxite, trine, and bemire. The alumina can have relatively high puritylike pseudoboehmite or can be a natural mineral like gibbsite orbauxite. Synthetic aluminas may also be used. Further, gamma alumina,theta alumina, and carbon supports can be effective.

An embodiment of the disclosure can be the sorbent that includes asupport and a metal compound selected from the group consisting ofalkali or alkaline earth. In an alternate embodiment, the sorbent canconsist essentially of the support and the metal compound, and anyassociated counterions. The metal compound can contain Li, Na, K, Rb,Cs, Be, Mg, Ca, Sr, or Ba, or a combination thereof; Li, Na, K, Mg, orCa, or can contain Na or K or a combination thereof. The metal compoundcan be at least about 5 wt % of the sorbent, at least about 7 wt %, atleast about 10 wt %, at least about 12 wt %, at least about 15 wt %, atleast about 17 wt %, at least about 20 wt % expressed as the wt %elemental concentration.

The support in the sorbent, alternatively called a substrate, can be anysupport one of ordinary skill in the art would select. In an embodiment,the support can be alumina, titania, zirconia, silica, clay, carbon andmixtures thereof. The support can be alumina. Generally, the supportshould have a high surface area and pore volume in order optimize theloading levels that the sorbent can demonstrate for CO₂. In anembodiment, the support can have a surface area of at least about 100m²/g, at least about 150 m²/g, at least about 200 m²/g, at least about250 m²/g, or at least about 300 m²/g. In an embodiment the support canhave a surface area of less than about 1200 m²/g, or less than about1000 m²/g.

An embodiment of the disclosure can also be a CO₂ adsorption sorbent,analogous to the disclosure above, wherein the CO₂ adsroption sorbentcan adsorb and desorb CO₂ under concentration swing conditions in thepresence of water, and without temperature or pressure changes.

An embodiment of the disclosure can also be a sorbent comprising a metalcompound and a support, wherein the sorbent adsorbs carbon dioxide froma wet atmosphere. The sorbent can adsorb the carbon dioxide from the wetatmosphere having up to 35 wt % water, or can adsorb the carbon dioxideand desorb water previously adsorbed from a higher water concentrationstream in a wet atmosphere having up to 35% water or less. In anembodiment, the sorbent can adsorb carbon dioxide after the sorbent hasbeen saturated with water at a partial pressure of 1 bar. Furthermore,because the sorbent can operate in a concentration swing system, thesorbent can also desorb carbon dioxide in an atmosphere that is greaterthan 60% water, or can desorb carbon dioxide from the sorbent previouslyloaded with carbon dioxide at a partial pressure of 0.02 to 1.0 bar.Thus, the CO₂ concentration in the incoming water stream, e.g. at aninlet to the sorbent in a regeneration/desorption point, can be lessthan the CO₂ concentration of the outgoing water stream, i.e. at anoutlet from the sorbent.

As discussed above with respect to the non-limiting surface equilibria,the sorbents of this disclosure can also be CO₂/H₂O equilibriumsorbents, where the sorbent will adsorb or desorb carbon dioxide andwater, depending on conditions as discussed in this disclosure. Thus,the disclosure also includes a sorbent composed of the metal compoundand a support, where the sorbent has a greater capacity for carbondioxide than the support, the sorbent has a greater capacity for waterthan the support, and the ratio of carbon dioxide and water on thesupport varies with the relative concentration of the two sorbates inthe environment above the sorbent. The sorbent can adsorb CO₂ in thepresence of less than 35% water at a pressure of one bar, and can desorbCO₂ in the presence of greater than 60% water vapor at a pressure of onebar.

The adsorptive capacity, or loading, of the sorbent has been describedwith respect to the amount of carbon dioxide that the sorbent canadsorb. Because to the equilibrium conditions the sorbent can operateunder during concentration swing adsorption and desorptive andadsorptive displacement, the sorbent can also be described as having awater capacity or loading. In an embodiment, the sorbent can have awater capacity of at least about 1.0 wt %, at least about 1.2 wt %, atleast about 1.5 wt %, at least about 1.7 wt %, or at least about 2.0 wt%. In an embodiment, the water capacity can be at least about 2.5 wt %,at least about 2.7 wt %, at least about 3.0 wt %, or at least about 3.5wt %. Thus, in an embodiment, the sorbent can described asadsorption-desorption sorbent composed of a metal compound and asupport, where the sorbent has a carbon dioxide capacity of at leastabout 0.5 wt %, a water capacity of at least about 1 wt %, and awater/carbon dioxide selectivity that varies with the relativeconcentration of the two sorbates in the environment above the sorbent.The sorbent has a carbon dioxide capacity of at least 0.7 wt %, or atleast 1.0 wt %. The sorbent can have has a water capacity of at leastabout 1.5 wt %, or at least about 2 wt %. The sorbent can have a watercapacity of less than about 20 wt %.

An embodiment of the disclosure can also include a carbon dioxide-waterequilibrium adsorption surface, comprising a metal compound adhered tothe surface of a support. The surface can adsorb carbon dioxide anddesorb water in a CO₂-water atmosphere having less than 35 wt % water,and can desorb carbon dioxide and adsorbed water in a CO₂-wateratmosphere having greater than 60 wt % water.

An embodiment of the disclosure can also include a CO₂ adsorptionsorbent having CO₂ adsorbed to the surface. The sorbent can include asupport, a metal compound comprising Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr,or Ba, or a combination thereof, and adsorbed carbon dioxide. The metalcompound can be at least 5 wt % of the sorbent, and the adsorbed carbondioxide can be at least 0.7 wt %, at least 1.0 wt % wt, or at least 1.5wt %. The adsorbed carbon dioxide in the sorbent can be any of theweight % loadings listed above. In an embodiment, the wt % carbondioxide adsorbed to the sorbent can be based on an adsorption stepoccurring at about standard pressure and at about 140° C.

An embodiment of the disclosure can include several methods of makingthe sorbent. The method can include incipient wetness impregnation (orcapillary impregnation) of a support, or a slurry/calcinations methodwhere the support is mixed with a solution containing the alkali oralkaline species, dried, and calcined in air to higher temperatures.

In an embodiment, the method can include treating a support with asolution comprising a metal complex and a solvent, and drying thesorbent. The solution can also consist essentially the metal complex andthe solvent. The support can be treated with volume of solution that isapproximately equal to the pore volume of the support. Approximatelyequal can mean an amount of liquid that one of ordinary skill in the artwould apply in an incipient wetness technique. For example, the supportcan have a known pore volume, and the support can be treated with anapproximately equal volume of the metal solution. The method can furtherinclude the step of calcining the sorbent at a temperature of at leastabout 350° C., at least about 400° C., at least about 450° C., at leastabout 500° C., at least about 550° C., or at least about 600° C. Thecalcining step can be at a temperature of less than about 1200° C., orless than about 1000° C. The calcining step can also include an air flowacross the support at a rate of about 3 volume/volume of solid/minute,about 4 volume/volume of solid/minute, or about 5 volume/volume ofsolid/minute.

In an embodiment, a method for making the sorbent include preparingpellets of a support by mixing the support in water, drying, and firingat least at about 300° C., mixing the pellets in an aqueous solutioncomprising water and a metal complex to prepare a pre-sorbent, dryingthe pre-sorbent, and calcining the pre-sorbent at temperature of atleast about 400° C. The pellets may be made by compression pelletizingor extrusion or other techniques known to those skilled in the art.

In an embodiment, the alkali or alkaline species may be admixed with thesupport material in a slurry and the slurry prepared into extrudates orpellets, dried, and calcined to a temperature of at least 300° C. Anadmixed pellet or extrudate formed in this manner may optionally haveadditional alkali or alkaline species added using the incipient wetnessmethods described above.

In an embodiment, the metal complex in the method can be an alkali oralkaline earth metal ion complexed with a counterion. The counterion canbe any counterion used by one of ordinary skill in the art, includingoxides, hydroxides, carbonates, bicarbonates or hydrates. In anembodiment, the metal complex is an organometallic complex, wherein thecounterion is an organic ion. The metal complex can be an acetate orcitrate complex with alkali or alkaline metal. The metal complex can bean acetate or citrate complex with Na or K.

Each of the sorbent compositions noted herein, and sorbents made by thedisclosed methods, can be applied to the adsorption/desorption processfor CO₂ discussed herein. The compositions can be used in concentrationswing processes, and processes using the compositions do not need torely on either temperature swing or pressure swing adsorption cycles toachieve a CO₂ separation process.

In an embodiment of the disclosure, the adsorption process can beapplied to single stage CO₂ adsorption system. The adsorption system caninclude a means for contacting the feed gas with the sorbent and meansfor alternating applying steam to the sorbent. The system can alsoinclude any desired purge and recycle streams steps. In addition, thesystem can include procedures for minimizing the steam requirement andefficient energy management.

At the start of the adsorption process, a sorbent bed may be highlyloaded with adsorbed water. As CO₂ from the feed stream is adsorbed,water is displaced as well as being partial pressure purged from the bedby the non-adsorbed components of the feed gas. Thus, the first effluentduring adsorption will be enriched in water vapor. Optionally, thisinitial portion may be diverted for recycle or other processoptimization. As the adsorbed CO₂ front continues moving through thebed, the point will be reached where CO₂ breaks through into theeffluent. Thus, a CO₂ lean effluent may be collected. The lean CO₂effluent can be used to rehydrate the regeneration bed(s) in a recycleor other process optimization design.

In the initial regeneration of CO₂ loaded bed, the first effluent can becomposed of the void gas contained in the bed herein the void gas refersto the non-adsorbed residual gases from the feed. Without limiting thisdisclosure a particular mechanistic hypothesis this may be understood byconsidering that water is adsorbed onto the bed in a well defined movingfront displacing CO₂ from the adsorbent and pushing the CO₂ ahead of it.The advancing wave of concentrating CO₂ further pushes ahead of it thenon-adsorbed void gases, which may also contain a lower concentration ofCO₂ and moisture. Thus, as the front advances the first effluent will bevoid gases and thus they can be diverted separate from the followingeffluent. The next effluent will be predominantly contain the displacedCO₂ at higher concentration due to the fact that the water is stillbeing adsorbed on the bed and thus the CO₂ while containing somemoisture will be at significantly higher concentration than it was inthe feed. This feature can distinguish the process from a conventionalstripping or partial pressure purge desorption. Following the CO₂ richeffluent, the stream breaks through the bed and further strips the CO₂off the sorbent.

A non limiting example of the feed gas composition exiting a bed,collected in a small lab sized cyclic adsorption unit is shown in FIG.1, where a simulated flue gas composed of 6% CO₂ in N₂ was adsorbed andthen steam regenerated. The example was run with the bed heldessentially isothermal at ˜140° C. and at ambient pressure.

Regeneration or desorption of CO₂ with steam can be single stage orcounter-current gas/solid multi-stage. Single stage or counter-currentgas/solid multi-stage processes can be carried out in various reactorvessel configurations known to those skilled the art. Such may includemoving beds, rotating wheel configurations, simulated moving beds, andsuch.

In view of the disclosure of the process and compositions described forCO₂ adsorption and desorption, several process configurations can beconstructed that capitalize on several advantages that the processdescribes.

A basic CO₂ separation system, 200, optionally called Capture, Displace,Strip (CDS), is shown schematically in FIG. 2. The CO₂ separation systemcan include can include one or more sorbent beds 201, which is capableof adsorbing and desorbing CO₂. The CO₂ separation system can include anadsorption zone 202, a CO₂ desorption zone 203, and optionally a purgingstage 204. In the CO₂ separation system, the sorbent bed or beds 201 canrotate through each of the stages 202, 203, and optionally 204. In thesystem, CO₂ from a CO₂ feed stream, e.g. a flue gas, is passed across asorbent bed, in this case two sorbent beds run staggered in time. Theuse of multiple beds on feed can be done as a way to manage pressuredrop, but a single bed per stage is also disclosed. The CO₂ is adsorbedfrom a CO₂ feed stream. As shown in FIG. 1, the adsorption zone can alsoinclude an adsorbent inlet 205 into which the CO₂ feed stream enters,and an adsorbent stage outlet 206, from which a purified feed stream,which has been depleted or purified of CO₂, exits. A next step in thecycle can be to introduce steam for regeneration in the desorption zone203 (or alternatively a regeneration zone.) As previously described, theinitial effluent upon steam introduction can be primarily comprised ofvoid gases. These gases can be diverted as shown to the atmosphere, oroptionally recycled to the feed gas. At a point in the steamregeneration the effluent would be diverted to further CO₂ purificationand compression. Thus, steam can enter the desorption zone 203 viadesorption inlet 207, and the effluent gas can exit the desorption zone203 via desorption outlet 208. One of ordinary skill would recognizethat a valve, not shown, can divert the outlet gas to either route,depending on if it is void gas via the optional discharge or the CO₂enriched stream. Following the discharge of the high concentration CO₂effluent portion of the regeneration, rather than the continued use ofsteam to further partial pressure strip the residual CO₂ from the bed,an optional purging stage 204 can be incorporated to strip the bed with,for example, ambient air. The effluent from this stripping can beadvantageously used in a power generation environment to be used as aportion of the combustion air. As would be apparent to those skilled inthe art, multiple simultaneous or sequential beds can be used at eachstep. Indeed, having several beds, staggered in time in the steamregeneration step would have the beneficial effect of smoothing the flowrate to the CO₂ compression step.

Thus, an embodiment of the disclosure includes a CO₂ separation systemthat includes a CO₂ adsorption zone, a CO₂ desorption zone, one or moreCO₂ sorbent beds, and a CO₂ feed stream. The sorbent bed can alternatebetween the adsorption zone and the desorption zone, and can adsorb CO₂from the CO₂ feed stream in the adsorption zone and desorb CO₂ in thedesorption zone. The system can include an inlet and an outlet for theadsorption zone where the CO₂ feed stream enters the adsorption zone viathe inlet and a purified feed stream exits the adsorption zone via theoutlet. The system can also include an inlet and an outlet for thedesorption zone, wherein a stream comprising steam enters the desorptionzone via the inlet and a CO₂ enriched stream exits via the outlet. Asexemplified by FIG. 2, the system can also include a purging stage afterthe desorption zone, wherein the sorbent bed enters the purge stage andis purged via a stripping gas stream.

The system can include more than one sorbent bed, including at least twosorbent beds, at least three sorbent beds, at least four sorbent beds,at least five sorbent beds, at least six or more sorbent beds. Thesorbent beds can rotate through each of the adsorption zone, desorptionzone, and optionally though a purge stage after the desorption zone. Thesorbent beds can include a sorbent, and the sorbent can include asubstrate and at least one alkali or alkaline earth component. As notedabove, the sorbent can be an alumina component and at least one alkalior alkaline earth component.

As discussed above, the CO₂ separation system does not rely on apressure swing or a temperature swing adsorption process, but can bedriven by concentration swing adsorption/desorption andadsorptive/desorptive displacement. The adsorption zone operates as aconcentration swing process and adsorptive displacement process, and thedesorption zone operates as a concentration swing and desorptivedisplacement process. The entire system can be run isothermally and at aconstant pressure.

As shown in FIG. 2, the adsorption inlet the adsorption inlet andadsorption outlet can be in opposing positions from the desorption inletand the desorption outlet, relative to the sorbent bed as the bedrotates through the zones.

In an embodiment of the disclosure, the processes, methods and systemscan be developed into a simulated moving bed system, in which sorbentbeds are stationary, but the flow of gas into and out of the sorbentbeds is scheduled such that a simulated moving bed system is created. Byway of example, a five bed simulated moving bed schematic is set forthin FIGS. 3A to 3F. Thus, a countercurrent movement of gas and solids canbe simulated using a number of stationary contactors with appropriatearrangement of valves and valve timing.

A feature of this counter-flow design is that, as the gas travelsthrough the sorbent, it encounters fresher (more recently desorbed)sorbent. At the exit of the reactor the gas stream is in contact withsorbent that has just come from the regeneration mode. This countercurrent design can provide a driving force to capture a higherpercentage of the component gas of interest. This disclosure can thenincrease the loading with a sorbent whose loading level is controlled bythe concentration gradient. For example, sorbents can adsorb more CO₂ athigher concentrations and less at low concentrations. A counter-flowdesign maximizes the loading by having the sorbent in contact with freshgas stream (with the highest gas concentration) just prior to going toregeneration mode.

For this disclosure, a configuration of simulated moving beds can employa number of stationary contactors. At any one time, some of thecontactors can have combustion gas flowing simultaneously in parallelwhile the other contactors can be exposed to steam flowing in series inthe direction opposite to that used for the combustion gas. Atintervals, valves are opened and closed to move the relative positionsof the contactors one step so that the contactor exposed to combustiongas the longest is now being steamed, and the contactor steamed thelongest is now exposed to combustion gas. A series of such stepscomprises a complete cycle bringing the contactors back to theirstarting positions. An example using 8 contactors is shown in FIGS. 4Ato 4F. There are 5 different valve positions (shown in Table 1) for abed, depending on where that bed is in the cycle. The overall cyclecomprises 8 steps. The valve pattern for each bed in each step isdescribed in Table 2.

TABLE 1 Valve Position Patterns Valve Name A B C D E (FIG. 4A) (FIG. 4B)(FIG. 4C) (FIG. 4D) (FIG. 4E) (FIG. 4F) FG Closed Closed Open ClosedClosed Purge In Series Closed Closed Open Open Closed Steam In Steam InClosed Closed Closed Closed Open Steam Side Closed Closed Open Open OpenBlock Valve GFG Side Open Open Closed Closed Closed Block Valve GFG OutC then O Open Closed Closed Closed GFG O then C Closed Closed ClosedClosed Purge Out Regen Closed Closed O then C Closed Closed Purge OutProduct Out Closed Closed C then O Closed Closed Series Closed ClosedClosed Open Open Steam Out Product Side Closed Closed Open Closed ClosedBlock Valve FG In Open Open Closed Closed Closed

TABLE 2 Valve Position Patterns versus Step Number Bed Step NumberNumber I II III IV V VI VII VIII 1 A B B C D D D E 2 B B C D D D E A 3 BC D D D E A B 4 C D D D E A B B 5 D D D E A B B C 6 D D E A B B C D 7 DE A B B C D D 8 E A B B C D D D

Another example using eight contactors with three on combustion gas andfive on steam is illustrated in FIG. 5A, and a representative valvelisting is in FIG. 5B. The valve schedule is then set forth in Table 3.An example of an 8 bed process is set forth in Example 8, below.

TABLE 3 Valve Opening and Closing Timing for 8-Bed configuration of FIG.5A and 5B Step Number in 8-Step Cycle 1 2 3 4 5 6 7 8 Bed A FG valve AOPEN CLOSED CLOSED CLOSED CLOSED CLOSED OPEN OPEN GFG valve A OPENCLOSED CLOSED CLOSED CLOSED CLOSED O, THEN C OPEN GFG purge valve ACLOSED CLOSED CLOSED CLOSED CLOSED CLOSED O, THEN C OPEN Steam valve ACLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CO2 valve ACLOSED C, THEN O CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CO2 purgevalve A CLOSED O, THEN C CLOSED CLOSED CLOSED CLOSED CLOSED CLOSEDSeries valve A-B CLOSED CLOSED OPEN OPEN OPEN OPEN CLOSED CLOSED Bed BFG valve B OPEN OPEN CLOSED CLOSED CLOSED CLOSED CLOSED OPEN GFG valve BOPEN OPEN CLOSED CLOSED CLOSED CLOSED CLOSED C, THEN O GFG purge valve BCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED O, THEN C Steam valve BCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED OPEN CLOSED CO2 valve B CLOSEDCLOSED C, THEN O CLOSED CLOSED CLOSED CLOSED CLOSED CO2 purge valve BCLOSED CLOSED O, THEN C CLOSED CLOSED CLOSED CLOSED CLOSED Series valveB-C CLOSED CLOSED CLOSED OPEN OPEN OPEN OPEN CLOSED Bed C FG valve COPEN OPEN OPEN CLOSED CLOSED CLOSED CLOSED CLOSED GFG valve C C, THEN OOPEN OPEN CLOSED CLOSED CLOSED CLOSED CLOSED GFG purge valve C O, THEN CCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED Steam valve C CLOSEDCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED OPEN CO2 valve C CLOSED CLOSEDCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CO2 purge valve C CLOSEDCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED Series valve C-D CLOSEDCLOSED CLOSED CLOSED OPEN OPEN OPEN OPEN Bed D FG valve D CLOSED OPENOPEN OPEN CLOSED CLOSED CLOSED CLOSED GFG valve D CLOSED C, THEN O OPENOPEN CLOSED CLOSED CLOSED CLOSED GFG purge valve D CLOSED O, THEN CCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED Steam valve D OPEN CLOSEDCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CO2 valve D CLOSED CLOSEDCLOSED CLOSED C, THEN O CLOSED CLOSED CLOSED CO2 purge valve D CLOSEDCLOSED CLOSED CLOSED O, THEN C CLOSED CLOSED CLOSED Series valve D-EOPEN CLOSED CLOSED CLOSED CLOSED OPEN OPEN OPEN Bed E FG valve E CLOSEDCLOSED OPEN OPEN OPEN CLOSED CLOSED CLOSED GFG valve E CLOSED CLOSED C,THEN O OPEN OPEN CLOSED CLOSED CLOSED GFG purge valve E CLOSED CLOSED O,THEN C CLOSED CLOSED CLOSED CLOSED CLOSED Steam valve E CLOSED OPENCLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CO2 valve E CLOSED CLOSEDCLOSED CLOSED CLOSED C, THEN O CLOSED CLOSED CO2 purge valve E CLOSEDCLOSED CLOSED CLOSED CLOSED O, THEN C CLOSED CLOSED Series valve E-FOPEN OPEN CLOSED CLOSED CLOSED CLOSED OPEN OPEN Bed F FG valve F CLOSEDCLOSED CLOSED OPEN OPEN OPEN CLOSED CLOSED GFG valve F CLOSED CLOSEDCLOSED C, THEN O OPEN OPEN CLOSED CLOSED GFG purge valve F CLOSED CLOSEDCLOSED O, THEN C CLOSED CLOSED CLOSED CLOSED Steam valve F CLOSED CLOSEDOPEN CLOSED CLOSED CLOSED CLOSED CLOSED CO2 valve F CLOSED CLOSED CLOSEDCLOSED CLOSED CLOSE C, THEN O CLOSED CO2 purge valve F CLOSED CLOSEDCLOSED CLOSED CLOSED CLOSED O, THEN C CLOSED Series valve F-G OPEN OPENOPEN CLOSED CLOSED CLOSED CLOSED OPEN Bed G FG valve G CLOSED CLOSEDCLOSED CLOSED OPEN OPEN OPEN CLOSED GFG valve G CLOSED CLOSED CLOSEDCLOSED C, THEN O OPEN OPEN CLOSED GFG purge valve G CLOSED CLOSED CLOSEDCLOSED O, THEN C CLOSED CLOSED CLOSED Steam valve G CLOSED CLOSED CLOSEDOPEN CLOSED CLOSED CLOSED CLOSED CO2 valve G CLOSED CLOSED CLOSED CLOSEDCLOSED CLOSED CLOSED C, THEN O CO2 purge valve G CLOSED CLOSED CLOSEDCLOSED CLOSED CLOSED CLOSED O, THEN C Series valve G-H OPEN OPEN OPENOPEN CLOSOED CLOSED CLOSED CLOSED Bed H FG valve H CLOSED CLOSED CLOSEDCLOSED CLOSED OPEN OPEN OPEN GFG valve H CLOSED CLOSED CLOSED CLOSEDCLOSED C, THEN O OPEN OPEN GFG purge valve H CLOSED CLOSED CLOSED CLOSEDCLOSED O, THEN C CLOSED CLOSED Steam valve H CLOSED CLOSED CLOSED CLOSEDOPEN CLOSED CLOSED CLOSED CO2 valve H C, THEN O CLOSED CLOSED CLOSEDCLOSED CLOSED CLOSED CLOSED CO2 purge valve H O, THEN C CLOSED CLOSEDCLOSED CLOSED CLOSED CLOSED CLOSED Series valve H-A CLOSED OPEN OPENOPEN OPEN CLOSED CLOSED CLOSED

The simulated moving beds of this disclosure can also be described bythe FIG. 6 and the discussion herein. A simulated moving bed system 600can be a series of fixed sorbent beds (not shown) which “rotate” throughseveral adsorption positions, such as 601, 602, and 611 and severaldesorption positions, such as 621, 622, and 631. These fixed beds rotatethrough each of the positions via a series of valves and lines thatinterconnect each of the beds, and the advancement of the bed throughthe adsorption and desorption positions and the flow of gases acrossthose beds can be controlled in such a fashion that the fixed bedsbecome part of a simulated moving bed system.

In the simulated moving bed system 600, a sorbent bed can move throughthe first adsorption position 601, having a second CO₂ feed stream 604and a second CO₂-depleted stream 606, to a second adsorption position602, having a first CO₂ feed stream 603 and a first CO₂-depleted stream605. The first and second adsorption positions are designated as suchbecause that can typically be the order in which the bed progressesthrough them. The first adsorption position can have the second CO₂ feedstream and the second CO₂ depleted stream, while the second adsorptionposition can have the first feed and first depleted streams. Thedesignation of first and second in this instance should not be viewed asa restrictive order for the feeds or streams, but instead as a numericaldesignation. In some embodiments, the gas streams in the adsorptionzone, which would include the first and second adsorption positions, canflow in series such that a first CO₂ feed stream 603 enters the secondadsorption position 602, and a first CO₂-depleted stream 605 from thesecond position could be transferred via lines and valves to become thesecond CO₂ feed stream 604 that enters the first adsorption position 601and exits as the second CO₂-depleted stream, 606. Such an order can havea countercurrent effect that allows the higher concentration of feed gasto enter the more saturated bed in the second position, and then flow tothe less saturated bed in the first position. In this case the bedpositions advance in the opposite direction of the gas flow. However, inanother embodiment, the two adsorption positions can be run in parallelwith the first and second feed streams 603 and 604 coming from a commonsource, i.e. a flue gas, with each bed receiving the same concentrationof CO₂ in the feed gas. The resulting CO₂-depleted streams 605 and 606can then be combined to form a final depleted gas stream which can besent to other processes or released via, for example, a flue stack.

After the second adsorption position 602, the sorbent bed can move intothe desorption zone, also called the regeneration zone. The sorbent bedcan enter the first desorption position 621, having a secondregeneration stream 624 and a second CO₂-enriched stream 626, then moveon to the second desorption position 622, having a first regenerationstream 623 and a first CO₂-enriched stream 625. As in the adsorptionzone, the designation of first and second desorption position canindicate how the bed progresses through the regeneration system. Thefirst desorption position can have the second regeneration stream andthe second CO₂-enriched stream, while the second adsorption position canhave has the first regeneration feed and first CO₂ enriched streams. Thedesignation of first and second in this instance should not be viewed asa restrictive order for the feeds or streams, but instead as a numericaldesignation. In some embodiments, the gas streams in the desorptionzone, which would include the first and second desorption positions, canflow in series such that the first CO₂-enriched stream 625 exits thesecond desorption position 622 enters the first desorption 621 as thesecond regeneration stream 624. Similarly, the regeneration positionscould also be operated in parallel.

While the structures in FIG. 6 show two adsorption positions and twodesorption positions, the disclosure herein should not be limited toonly a four position system. The simulated moving bed system can alsoinclude additional beds, such as the additional earlier bed 611 on theadsorption side, and additional later position 631 on the desorptionside. Here, the terms earlier and later are determined based on thetiming of the progression of the beds through the system. In anon-limiting example, a sorbent bed could start at adsorption position611, then proceed to adsorption positions 601 and 602, then onto thedesorption positions 621, 622 and 631, before returning to adsorptionposition 611. Alternatively, bed 611 might instead represent a purgeposition, such that the bed would start at adsorption position 601, thenproceed to adsorption position 602, then onto the desorption positions621, 622 and 631, move through a purge position 611, and then return tothe first adsorption position 601. The simulated moving bed system caninclude 3 positions, 4 positions, 5 positions, 6 positions, 7,positions, 8 positions, 9 positions, or ten or more positions.

In view of the discussion of simulated moving beds and systems discussedabove, a method for separating and/or purifying a CO₂ gas from a CO₂feed can be described. In an embodiment, the method for the separationand/or purification of CO₂ gas from a CO₂ feed stream can includeproviding at least two adsorption positions and two desorptionpositions, and at least two fixed sorbent beds that progress through theadsorption and desorption positions. The first adsorption position canhave a second CO₂ stream and produce a second CO₂-depleted stream, andthe second adsorption position can have a first CO₂ stream and canproduce a first CO₂-depleted stream. The first desorption position canhave a second regeneration stream and can produce a second CO₂-enrichedstream, and the second desorption position can have a first regenerationstream and can produce a first CO₂-enriched stream. Each sorbent bed canhave a sorbent, a first port at an end of the bed and a second port atan end of the bed distal to the first port.

The first step of the method can include exposing the first sorbent bedto a second CO₂ stream at a first adsorption position, and the secondsorbent bed to a first CO₂ steam at the second adsorption position. Thesecond step can include exposing the first sorbent bed to the first CO₂stream at the second sorbent position and the second sorbent bed to thesecond regeneration stream at a first desorption position. The thirdstep can include exposing the first sorbent bed to the secondregeneration stream at the first desorption position and the secondsorbent bed to a first regeneration stream at a second regenerationposition. And, an optional fourth step can include exposing the secondsorbent bed to the second CO₂ stream at the first adsorption positionand the first sorbent bed to the first regeneration stream at the seconddesorption. The fourth step can instead include advancing the bedsthrough downstream desorption positions until each sorbent bed returnsto the beginning of the adsorption zone.

As discussed previously, the method can be conducted at substantiallyconstant temperature and substantially constant pressure with neither atemperature swing nor pressure swing. In an embodiment, the regenerationstreams comprise steam, or can be a steam stream.

In a further embodiment, the method can include providing a system ofvalves and lines connecting at least two fixed sorbent beds such that abed advances from a first adsorption position to a second adsorptionposition to a first desorption position to the second desorptionposition, and optionally back to the first adsorption position.

As noted previously, and as shown in some of the nonlimiting valveschedules shown above, the two or more adsorption positions can be runin parallel. In an embodiment, the CO₂-feed stream can be directed intoboth the first CO₂ stream of the second adsorption position and thesecond CO₂ stream of the first adsorption position such that the twoadsorption positions operate in parallel. The first and the second CO₂depleted streams from the second and first adsorption positions can alsobe combined together for collection or additional processing. In analternate embodiment, the two or more adsorption positions can be run inseries. Thus the first CO₂-depleted stream from the second adsorptionbed can b used as the second CO₂ stream in the first adsorption positionsuch that the two adsorption positions operate in series, and the secondCO₂-depleted stream is collected.

When a new sorbent bed assumes a first adsorption position, it can havean initial void gas, such as a residual steam stream after exiting thedesorption/regeneration stage. In one embodiment, the effluent from thesorbent bed can be diverted to a purging stage. In an alternative, thefirst adsorption position can include an optional purge. Thus, a firstportion of the second CO₂ depleted stream from the first adsorptionposition can be diverted as a purge stream before switching tocollection of the CO₂-depleted stream.

The purge stream can also be utilized as a part of the overall scheme asa recycled gas flow or alternate flow. In an embodiment, the stream,optionally a portion of the feed stream, can be introduced into a bedwhich just advanced out of the desorption zone, and the effluent fromthat bed can be directed to a bed which has just advanced out of theadsorption stage. A second effluent resulting from the bed which hasjust advanced out of the adsorption can be directed either to a stack orto be recycled within the system. A non-limiting example of this can bedemonstrated in FIG. 35. In an embodiment, the purge steps can includeintroducing a separate stream, optionally a portion of the feed streamor a non-adsorbing gas, into a bed which just advanced out of thedesorption zone, in order to push out the dead volume gas and adsorbedsteam of this bed back into a desorption zone bed. A non-limitingexample can be demonstrated in FIGS. 22 and 34.

In an embodiment of the disclosure, the desorption positions can be runin series. The first CO₂-enriched stream from the second desorptionposition can be used as the second regeneration stream in the firstdesorption position. In another embodiment, one or more desorptionpositions could be run outside of the series, such as one or more bedsbeing run in parallel, such as to remove residual CO₂ feed gas for arecycle stream. In an embodiment, the beds can be desorbed in parallel,and the resulting streams combined or selectively diverted, depending ongas content of the parallel streams.

Another aspect of the disclosure can be that the gas flows in adsorptionare conducted in one direction across the sorbent bed, but theregeneration can be advantageously conducted with flows in the oppositedirection. In an embodiment the CO₂ streams enter each sorbent bed inthe adsorption positions via the first port, and the CO₂-depleted streamexits via the second port. The regeneration streams enter each of thesorbent beds in the desorption positions via the second port, and theCO₂-enriched stream exits via the first port.

In view of the disclosure, a simulated moving bed system can bedescribed. In an embodiment, the simulated moving bed system for CO₂purification/separation can include a plurality of fixed sorbent beds,each sorbent bed comprising a sorbent, a first port at an end of the bedand a second port at an end of the bed distal to the first port; anadsorption zone and a desorption zone; and a series of valves and linesinterconnecting each of the beds via the first and second ports; a CO₂feed stream, a steam stream, a CO₂-depleted stream, and a CO₂-enrichedstream, and one or more purge streams. The system operates undersubstantially constant pressure and constant temperature with neithertemperature swing nor pressure swing

When a bed is in an adsorption position, the first port of the bed canbe connected to either the CO₂ feed stream or the second port of aanother sorbent bed in the adsorption zone which is generating a CO₂depleted stream. The second port of the bed can be either connected to afirst port of another bed, to a purge line, or to a unit collecting theCO₂-depleted stream or optionally diverted to purge for a portion oftime. Thus, the beds operating in an adsorption zone can operate inseries.

In an alternate embodiment, when any bed is in an adsorption position,the first port is connected to the CO₂ feed stream and the second portis connected to a unit collecting the CO₂-depleted stream, and bedearliest in the adsorption zone optionally connected to a purge line.Thus, all the beds operating in an adsorption zone can operate inparallel.

In the desorption, the beds operating in the desorption zone can operatein series. The bed in the desorption zone longest receives an initialregeneration stream, typically a steam stream, and each bed canconnected via a port to the bed next longest in the desorption zone. Thebed earliest in the desorption zone can emit via a port the CO₂-enrichedstream for collection or additional processing. When a bed is in adesorption position, the first port can be connected to the second portof another bed, and the second port can connected to the first port ofanother bed, with the exceptions that the second port of the bed longestin the desorption zone is connected to the steam stream, and the firstport of the bed earliest in the desorption zone is connected to a unitfor collecting the CO₂-enriched stream or optionally diverted to purgefor a portion of time. In a specific embodiment, the purge steps canconsist of introducing a separate stream, optionally a portion of thefeed stream, into a bed which just advanced out of the desorption zone,and directing the effluent to a bed which has just advanced out of theadsorption zone; directing the ultimate effluent either to a stack or tobe recycled within the system. In another specific embodiment, the purgesteps can consist of introducing a separate stream, optionally a portionof the feed stream or a non-adsorbing gas, into a bed which justadvanced out of the desorption zone, in order to push out the deadvolume gas and adsorbed steam of this bed back into a desorption zonebed.

The fixed adsorbent beds in the simulated moving bed system can have anyaspect ratio one of ordinary skill would include, where the aspect ratiois a measure of the length of the sorbent bed versus it width. In anembodiment, the aspect ratio should provide a superficial gas residencetime (flow in volume per unit of time divided by bed cross-sectionalarea) of at least 5 seconds.

In a simulated moving bed system, the system can have several beds thatalternate between an adsorption zone, a desorption zone, and optionallyone or more purge zones. The ratio of beds operating in an adsorptionzone can generally be equal to or less than the number of beds operatingin a desorption or regeneration zone. In an embodiment, the ratio ofbeds in adsorption to desorption is between about 1:1 and 1:5, betweenabout 1:1 and 1:4, between about 1:1 and 1:3, and between about 1:1 and1:2.

An embodiment of the disclosure can also include a counter-flow movingadsorber in a reactor, where the sorbent moves vertically down with thegas flow vertical up. (FIG. 7). The gas stream flows up through theadsorber bed (Reactor #1) counter current to the sorbent pellets whichfall vertically down through the bed. The sorbent pellets are circulatedthrough to the regeneration bed and back to the adsorber bed. Thesorbent can be transported by many mechanisms including pneumatictransport, screw conveyor and bucket elevator. Reactor #2, theregenerator, can be any moving bed design where the flow contact betweenthe sorbents and gases is counter current. It can be a reactor where thesorbent is transported up as the gas flows down. In another embodiment,the regenerator can also be another vertical falling moving bed.

An embodiment of the disclosure can also include a vertical flowingmoving bed, as illustrated in FIG. 8. The absorber bed design can be avertical falling moving bed with an insulated screw conveyor belt toconvey the solids through the steam stripper (regenerator). Flue gas canflow up through the adsorber bed counter current to the sorbent pelletswhich flows down. The solids can move up through the screw conveyor withthe steam flowing down in counter flow to remove the absorbed CO₂. Thescrew conveyor could comprise of vertical, inclined, or horizontalconveyors and/or combinations thereof.

An embodiment of the disclosure can also include a moving bed where thesolids are moved with a bucket elevator, as shown in FIG. 9. In thisembodiment, the adsorber bed and regenerator beds are both verticalfalling moving beds and a bucket elevator circulates the sorbent up tothe upper bed. In both beds the gas stream can move up while the sorbentcan fall down. The upper reactor is shown as the regenerator, however,the bed's location could also be reversed with the regeneration bed inthe upper position. The bucket elevator may comprise a centrifugaldischarge, or continuous discharge or a drag conveyor.

An embodiment of the disclosure can then be a circulating moving bedsystem having a sorbent, a CO₂ feed stream, a regeneration stream, anadsorption reactor and a desorption reactor. As shown in several of theprevious non-limiting examples, the system can include an adsorptionreactor and regeneration reactor. The adsorption reactor can have afirst entry point for the sorbent at an end of the adsorption reactor, asecond entry point for the CO₂ feed stream distal to the first entrypoint, a sorbent exit point for the sorbent proximal to the second entrypoint, and a feed stream exit point proximal to the first entry point.The regeneration reactor can have a first entry point for the sorbent atan end of the regeneration reactor, a second entry point for theregeneration stream distal to the first entry point, a sorbent exitpoint for the sorbent proximal to the second entry point, and aregeneration stream exit point proximal to the first entry point.

The moving bed systems can incorporate each of the discussions set forththroughout the application, including the lack of a temperature swing orpressure swing process, and the use of sorbents disclosed herein.

The moving bed systems of this disclosure can also include a sorbenttransport system to move sorbent between each reactor. As shown in somenon-limiting examples, the sorbent transport system can be included ineither the adsorption or regeneration reactor, or both, and can movesorbent in a direction opposite to the direction of either the CO₂ feedstream or the regeneration stream, respectively.

The moving bed systems of this disclosure can also be described as partof a process. In an embodiment of the disclosure, a process for theseparation and/or purification of CO₂ from a CO₂ feed stream can includeadsorbing the CO₂ on a sorbent by passing the CO₂ feed stream throughthe adsorption reactor, the adsorption reactor comprising a first entrypoint for the sorbent at an end of the adsorption reactor, a secondentry point for the CO₂ feed stream distal to the first entry point, asorbent exit point for the sorbent proximal to the second entry point,and a feed stream exit point proximal to the first entry point; anddesorbing the CO₂ from the sorbent in the regeneration reactor, theregeneration reactor comprising a first entry point for the sorbent atan end of the regeneration reactor, a second entry point for theregeneration stream distal to the first entry point, a sorbent exitpoint for the sorbent proximal to the second entry point, and aregeneration stream exit point proximal to the first entry point.

In an embodiment of the disclosure, the counter flow moving bed can alsobe a rotating moving bed where the sorbent is stationary inside a vesselwhich itself rotates such that the gas flows across it is in acounter-flow manner. The schematic diagram of such a counterflow movingbed is shown in FIG. 10. This bed rotates in a circle like a carousel.In contrast, other rotating wheel applications have gas flow that comesin from the top (roof) or bottom (floor) planes of the carousel. (U.S.Pat. Nos. 6,447,583, 5,503,222, 6,527,836). These rotating beds areessentially multiple fixed beds with a sliding seal instead of valves.In some other rotating wheel applications pressure swing is used as theregeneration mechanism. This type of rotating bed is essentially a setof fixed bed reactors. A fixed bed reactor must provide for both themass transfer zones and extra capacity to store sorbent. Since there isalways some residual gas in the reactor, very frequent cycling must beavoided to prevent contamination of one stream by the other.Consequently the fixed beds are about 3 to 5 times larger than thecounter-current rotating bed.

In an embodiment of this disclosure, the gas flows in the rotatingmoving bed from the sides of the rotating wheel as shown in anembodiment in FIG. 10. This flow path design enables counter currentcontact between the gas and the sorbent. The stream containing the gasto be removed runs across one section the wheel. On the other side theregeneration gas stream flows across. In this disclosure theregeneration is also by contact with another gas rather than pressureswing or temperature swing. There is a transition region between theadsorption and regeneration sections where the sorbent is sealed off tokeep the adsorption and regeneration spaces separate. The section of thesorbent that is in this transition region changes as the wheel rotates.A feature of the rotating wheel design is that the energy requirement tocirculate the sorbent is lower than for other sorbent circulationmethods such as pneumatic transport, screw conveyor, and bucketelevators. In contrast to the pneumatic transport, screw conveyor andbucket elevator, which move sorbent vertically, the rolling bed onrailroad wheels and tracks and the rolling bed on truck tires andconcrete needs to only move the material horizontally. There is asubstantial cost benefit to just overcoming the rolling friction ratherthan have to move solids up a vertical lift.

The efficiency benefits of counterflow contact are well established inthe design of regenerative heat exchangers which also use acounter-current flow design. Regenerative heat exchangers can have twofluids (generally the same fluid) following on each side in oppositeflow directions. The fluid flows to one side of the heat exchanger whereit can be heated (or cooled). After exiting the heat exchanger, it maygo through an external processing step, and then be flowed back throughthe heat exchanger in the opposite direction. In generally, the fluidwill cycle through one side of the heat exchanger, go through a processand then go back through the heat exchanger on the other side in theother direction. This is useful because with the counter current flow,the fluid incoming to a process is heated using the energy contained inthe fluid exiting this process. Thus, the regenerative heat exchangercan give a considerable net savings in energy, since most of the heatenergy is reclaimed nearly in a thermodynamically reversible way. Thistype of heat exchanger can have a thermal efficiency of over 90%,transferring almost all the relative heat energy from one flow directionto the other. Only a small amount of extra heat energy needs to be addedat the hot end, and dissipated at the cold end, even to maintain veryhigh or very low temperatures. The counter-current approach of theregenerative heat exchanger can be used in ad/absorbents process designto achieve a high efficiency. In this case, the gases flows are in acountercurrent manner and there is a concentration gradient rather thana temperature gradient driving the process.

An embodiment of the disclosure can also be a counter-flow rotatingwheel bed design with concentration swing. A schematic of the embodimentof this design for CO₂ capture from flue gas with steam strippingregeneration is shown in FIG. 12 along with a view of the exterior ofthe design, in FIG. 11. The combustion flue gas stream flows in from thesides of the rotating wheel as shown. The wheel rotates in the oppositedirection as the gas flow path. This provides counter current contactbetween the flue gas and the adsorbent. Flue gas flows horizontallyacross a section of the wheel and adsorbs CO₂. With the counter-flowdesign the flue gas with the lowest concentration for CO₂ near the gasflow exit is in contact with the most recently regenerated sorbent. Thisfeature enables the lowest concentration of CO₂ leaving the reactor. Onthe other section of the rotating wheel the regeneration steam flowsacross, also in a counter current path to the sorbent rotation directionand desorbs the CO₂ from the sorbent. With the counter current flow paththe most highly loaded adsorbent is in contact with the steam leavingthe reactor. This feature yields the highest possible CO₂ concentrationin the regeneration gas outlet.

There is a transition region between the adsorption and regenerationsections where the sorbent is sealed off to keep the adsorption andregeneration spaces separate, as shown in FIG. 13. The section ofsorbent that is in this transition region changes as the wheel rotates.In a non-limiting example, the rotating wheel can be made of 24 sorbentcells, and each cell could about 40 ft tall by 39 ft wide by 4 ft. Doorson each cell can allow gas to flow through or can close to seal offsections in the transition region. A schematic of the transition regionis show in above. Each transition zone isolates up to two sorbent cells.As the set of doors one cell opens up, the other sets of doors on theadjacent cell is still in place to block reverse flow. In thisembodiment, the opening and closing of these doors is activated by theflow of gas through the sorbent. Doors close in the transition regionbecause the pressure gradient is in the reverse direction. The doors aredesigned to not allow reverse flow. The doors are hinged and do not openmore than 85° by the hinge design. The sealing does not have to beperfect. With a 1/32 inch gap, the doors will stop >99.5% of the totalflow. The doors when closed are not perfectly sealed but are shimmedafter the sorbent is loaded to minimize the gap between the door and itsframe when closed. The interior vertical cross section showing thesedoors is shown above. There is also a set of doors on the side of therotating bed which are opened by mechanical means to allow flow into orout of the side of the rotating bed.

The rotating bed can be inside a non-moving exterior structure toprotect the internal reactor from weather, as shown in FIG. 14. Theexterior wall can be insulated on the outside to maintain thetemperature of the system. The non-moving screen at the top of thestructure allows air to move by natural convection and to keep thebottom part of the rotating moving bed near ambient temperature. Theconcrete roadway or floor provides the support for the rotating movingbed.

An embodiment of the current disclosure can then be a rotary moving bedassembly such as described above. The rotary moving bed can include arotational assembly having a vertical axis of rotation and a pluralityof fixed sorbent cells positioned horizontally relative to the axis ofrotation and each cell or a combination of cells filling the verticalspace within the rotational assembly such that air substantially cannotbypass the sorbent cells, a non-moving exterior structure; aregeneration stream inlet and outlet; and a CO₂ feed stream inlet andoutlet. One of ordinary skill would understand that substantially cannotbypass does not mean that no gas bypasses the sorbent cell, but that therotary bed is designed such that no bypass is intentionally designedinto the assembly. Some level of leakage and a lack of airtight fitmight be expected in constructing a rotary bed assembly of thedisclosure. The fixed sorbent cell rotates through the assembly in onedirection while the two gas flows travel in the opposite direction.Thus, a countercurrent flow for both adsorption and desorption can beestablished. Thus, in an embodiment, a regeneration stream can flow fromthe regeneration inlet to the regeneration outlet in the oppositedirection of rotation for the rotational assembly, and a CO₂ feed streamflows from the CO₂ feed stream inlet to the CO₂ feed stream outlet inthe opposite direction of rotation for the rotational assembly.

As demonstrated by the previous figures, an embodiment of the disclosurecan also include the CO₂ feed stream and the regeneration feed streamwhich flow in a horizontal direction relative to the vertical axis ofrotation. Note that this flow differs from the rotary bed processesdiscussed earlier in which the air flow was across the cells in avertical direction, leading to an overall ineffective use of space andsize of the beds. With the gas flow from inlet to outlet across thefixed beds, a region between the regeneration inlet and outlets can forma desorption zone and a region between the CO₂ feed stream inlet andoutlet form an adsorption zone. The adsorption zone can contain aplurality of sorbent cells in contact with CO₂ feed stream, and thesorbent cells in the desorption zone are moving in the oppositedirection from the feed stream. Similarly, the desorption zone cancontain a plurality of sorbent cells in contact with regenerationstream, and the sorbent cells in the desorption zone are moving in theopposite direction from the regeneration stream. As discussed, the gasflow across the multiple beds can occur in a countercurrent fashion,such that the beds with highest concentrations of adsorbed CO₂ areexposed to the feed gas with the highest CO₂ concentration, and lowerconcentration beds are exposed to feed gases with low amounts of CO₂ butcan still adsorb the CO₂ due to the large amount of capacity those bedshave.

The rotary moving bed also contains transition zones in the regionbetween the CO₂ feed stream outlet and the regeneration feed streaminlet and the region between the regeneration stream outlet and CO₂ feedstream inlet. Sorbent cells passing through these zones are not incontact with either the regeneration stream or the CO₂ feed stream.

Another embodiment of the disclosure can be length of time a sorbentcell spends in each zone, or a residence time. A sorbent cell can have aresidence time, measured as a percentage of time required to make onecycle around the rotating bed, in either the adsorption or desorptionzone of at least about 30% of one cycle, at least about 35% of onecycle, or at least about 40% of one cycle. Similarly, the residence timeof a sorbent cell in a transition zone is less than 20% of one cycle,less than 15% of one cycle, or less than 10% of one cycle.Alternatively, the length of time a sorbent cell spends in a zone can bedescribed with respect to the number of total sorbent cells in a givenzone at a specific point in time. In an embodiment, the adsorption zonecan have at least about 30% of the total sorbent cells in the zone, atleast 35% of the total sorbent cells, or at least 40% of the totalsorbent cells. Similarly, the desorption zone can have at least about30% of the total sorbent cells in the zone, at least 35% of the totalsorbent cells, or at least 40% of the total sorbent cells.

The sorbent cells of the rotary moving bed can contain the sorbent asdescribed and disclosed herein.

In an embodiment, the disclosure can also include a process for theseparation and/or purification of CO₂ gas from a CO₂ feed stream, whichincludes feeding a CO₂ containing feed stream into a CO₂ feed streaminlet of a rotary moving bed and collecting a CO₂-depleted feed streamat a CO₂ feed stream outlet of the rotary moving bed and feeding aregeneration stream into a regeneration stream inlet of the rotarymoving bed and collecting a CO₂-enriched stream at the regenerationstream outlet of the rotary moving bed, wherein the regeneration streamflows from the regeneration inlet to the regeneration outlet in theopposite direction of rotation for the rotational assembly, and the CO₂feed stream flows from the CO₂ feed stream inlet to the CO₂ feed streamoutlet in the opposite direction of rotation for the rotationalassembly. The rotary moving bed can be as described and disclosed.

In an alternate embodiment, the sorbent technology can alternatively beapplied to a rotary moving bed as shown in FIG. 15. The CO₂ feed streamand the regeneration stream each flow in a direction parallel to theaxis of rotation, e.g. a rotary moving bed rotating on a vertical axiswould have each stream flowing across the sorbent beds in a verticaldirection. Adsorption can be conducted on one portion of the rotarywheel, with the CO₂ feed stream flowing up through the sorbent beds, anddesorption/regeneration can be conducted on another portion of therotary wheel, with the regeneration stream flowing down through thesorbent beds. In an embodiment, the gas stream and the regenerationstream can flow in opposite directions, as shown in FIG. 15, or the twostreams can flow in the same direction. The portions of the wheel inregeneration or adsorption need not be equal.

In another embodiment, the rotary wheel can be arranged such thatcounter-current staging of gas flows and solids movement can beachieved, as shown in FIG. 16. The wheel is a fixed bed of sorbent whichrotates in the direction shown. The segments represent individualstationary ducts which lead gas flows into and out of the wheel. As thewheel rotates, the gas flows are led in directions counter to thedirection of rotation, thereby exposing the sorbent to concentrations ofthe carbon dioxide that improve utilization of the sorbent and minimizethe amount of displacing steam required.

In another embodiment, the simulated moving bed strategy discussed abovecan be applied to a rotary wheel by creating different flows of gas intoand out of different zones of the rotary wheel. As illustrated in FIG.17, the segments identified by different patterns represent divisions ofthe ducting leading into and out of the wheel, which is a fixed bed thatrotates in the direction shown by the arrow in the center. In thelegend, FG represents the flue gas being treated, and GFG the “green”low Carbon dioxide product. The lines connecting the segments representducts that recirculate the streams shown to other ducts.

In constructing the sorbent beds used within the methods, processes, andsystems of the disclosure, the sorbent can be placed in the beds usingany method known to one of ordinary skill in the art. In an embodiment,the sorbent can be contained as free particles that move through asystem in a countercurrent fashion, such as in the vertical moving bedsin FIG. 7 or 8. Alternatively, the sorbent can also be contained withindividual modules, such as the module of FIG. 18A. The sorbent can becontained in an individual module which is open at the top and having aperforated bottom to allow gas flow with retaining the sorbent. Thesorbent particles can then be contained as packed beds in the modules,and layered beds of modules can then be assembled using sorbent modulesand inter-bed spacers or flow channels as shown in FIG. 18B to producethe layered beds shown in FIG. 19A, viewed from the inlet and outletends, and FIG. 19B, viewed from the side. The layered beds can providefor high volume gas flow with low pressure drop. Gases introduce fromthe right flow down through the beds and out the left side; gasesintroduced from the left flow up and out the right side.

As an alternative to individual sorbent containing modules, it isenvisioned that a stacked bed configuration could also be achieved withsupport grids in each layer and loose adsorbent particles as extrudatesor other low pressure drop forms without the use of individual sorbentmodules.

Another configuration that provides the benefits of segmentationinvolves arranging the segments as vertical paced beds with flowchannels that provide for parallel horizontal flow of gases, asillustrated in FIG. 20. The beds are contained within screens mountedvertically. Adsorbent is filled from the top and dumped from the bottom.Process gas flow is in the top and out the bottom, or in the bottom andout the top. The flow divides into the channels between beds, goesthrough the beds and then out the channels to the other side andcollects to flow out.

EXAMPLES Example 1 Sorbent Preparation and Characterization

An alkalized alumina adsorbent was prepared from alumina powder(boehmite) and sodium carbonate. The boehmite and sodium carbonate weremixed in distilled water. The resulting solution was filtered andsediment dried. This sediment mixed with a nitric acid solution wasextruded into pellets and fired.

As an example of a sample preparation, 210 g Boehmite V-700 (UOP), 132 gNa₂CO₃ and 900 ml H₂O were mixed at 90° C. for 2 hours. The resultingsolution was filtered, and the sediment was left to dry over night atroom temperature. First, 380 g of the sediment material were put in thedrying oven for 3.5 hours. Next, 309.4 g of the dried material weremixed with 163 ml of the HNO₃ solution (0.75 ml HNO₃/20 ml H₂O). Pelletswere extruded to ⅛″ diameter pellets, dried at room temperature and thencalcined with heating from room temperature up to 100° C. at 0.2°C./min. for 2 hours and then heating 100° C. up to 650° C. at 0.5°C./min. for 4 hours.

This sorbent was characterized in a fixed bed where it was cycled undersimulated coal flue gas (13.7% CO₂ 9.0% H₂O with the balance N₂) andregenerated with 1 atm of steam. The fixed bed was operated in a counterflow mode with the simulated flue run down and the steam flow up throughthe reactor. The GHSV of the simulated flue gas was 2500 hr⁻¹ during the2 minute adsorption step and the GHSV of the steam was 2500 hr⁻¹ duringthe 4 minute regeneration step. The adsorbent had a dynamic CO₂ loadingcapacity 0.8 wt %.

Example 2 Sorbent Preparation and Characterization

An alkalized alumina adsorbent was prepared from alumina powder(boehmite) and sodium bicarbonate. The boehmite and sodium bicarbonatewere mixed in distilled water. The resulting solution was allowed tosettle, the solution decanted off and the precipitate dried. Theprecipitate was extruded into pellets with a sodium nitrate solution andfired. As an example of a sample preparation, 8903 g Boehmite Versal-700(UOP), 5594 g NaHCO₃, and 38.1 L H₂O were mixed at room temperature for18 hours. The solution was then allowed to settle and the excesssolution was decanted off. The precipitate was dried at 150° F. Driedpowder (8700 g) were mixed with 2% Methocel F4M (Dow) (174 g) and thencombined with 8265 g of 3.75% NaNO3 solution. This material was extrudedto ⅛″ pellets and air dried overnight and then fired at 400° C. for 4hours.

This sorbent was characterized in a fixed bed where it was cycled undersimulated natural gas flue gas (4.1% CO₂, 8.3% H₂O with the balance N₂)and regenerated with 100% steam at ambient pressure, as shown in FIG. 21(CO₂ feed and effluent flow rates under cycling with 4.1% CO₂, 8.3% H₂Osimulated flue gas (GHSV 2080 hr⁻¹) and steam regeneration (GHSV 1280hr⁻¹). Temperature decreases during adsorption of CO₂ from flue gas andtemperature increased with CO₂ desorption during steam regeneration.Dynamic CO₂ loading capacity is 0.7 wt %. Adsorbent prepared accordingto adsorbent preparation Example 2.) The fixed bed was operated in acounter flow mode with the simulated flue run down and the steam flow upthrough the reactor. The GHSV of the simulated flue gas was 2080 hr⁻¹during the 11 minute adsorption step and the GHSV of the steam was 1280hr⁻¹ during the 13 minute regeneration step. The adsorbent had a dynamicCO₂ loading capacity of 0.7 wt %. As is characteristic of this processwithout the removal of heat from the bed, the temperature duringadsorption of CO₂ from the flue gas was lower at 140° C. and duringregeneration it rose to 160° C. It steadily oscillated between thesetemperatures.

Example 3 Sorbent Preparation and Characterization

An alkalized alumina adsorbent was prepared from alumina powder(gibbsite) and sodium bicarbonate. The boehmite and sodium bicarbonatewere mixed in distilled water. The resulting solution was filtered andprecipitate dried. This precipitate was mixed with a methocel FM andVolclay and was extruded with Boehmite solution (6.7% conc) into pelletsand fired.

As an example of a sample preparation, 153.5 g Alcan WH31 (Alcan) whichhad been fired at 275° C. for 8 hr, 96.5 g NaHCO₃ and 657.5 ml H₂O weremixed at 90° C. for 1 hours. The resulting solution was filtered, andthe filtrate was left to dry over night at room temperature and thendried at 100° C. for 1 hours. 150 g of the dried material were dry mixedwith Volclay 353 CER (American Colloid Company) (16.7 g) and MethocelF4M (Dow) (3.34 g) and then mixed with 93.52 g of the Boehmite solution(6.7% conc). Pellets were extruded to 1/16″ diameter pellets, dried atroom temperature and then calcined at 550° C. for 4 hours.

This adsorbent was characterized in a fixed bed where it was cycledunder simulated coal gas flue gas (12.3% CO₂, 13.8% H₂O with the balanceN₂) and regenerated with 1 atm steam. The fixed bed was operated in acounter flow mode with the simulated flue run down and the steam flow upthrough the reactor. The GHSV of the simulated flue gas was 1900 hr⁻¹during the 5 minute adsorption step and the GHSV of the steam was 900hr⁻¹ during the 10 minute regeneration step. The adsorbent had a dynamicCO₂ loading capacity 0.57 wt %. As is characteristic of the processwithout the removal of heat the temperature during adsorption of CO₂from the flue gas was lower at 191° C. and during regeneration itincreased to 198° C. It steadily oscillated between these temperatures.

Example 4 Sorbent Preparation

The methods of/composition of the adsorbent in examples 1 and 2 can beextended to other alkalized alumina adsorbent compositions.

The methods of/of the adsorbent examples 1 and 2 where the firstcomponent is any alkali or alkaline earth metal. A further example iswhere the adsorbent is comprised of sodium carbonate or soda ash(Na₂CO₃), potassium carbonate, trona (trisodium hydrogendicarbonatealcinati Na₃H(CO₃)₂.2H₂O), baking soda (NaHCO₃). Sodium aluminate(2NaAlO₂═Na₂O*Al₂O₃), gamma (γ)-Alumina {Al₂O₃(G)}, hydrated alumina(Boehmite, Al₂O₃*H₂O), Gibbsite, Bauxite, sodium aluminate, calciumsilicate (e.g. portland cement). Some low Gibbsites that can be used areAlcan H10 ($84/ton), Alcan WH31 ($133/ton), and Alcan OP-25 ($135/ton).

Example 5 Sorbent Preparation

γ-Al₂O₃ extrudates were used as support to deposit Na₂CO₃. It hassurface area of 306 m²/g, 0.85 cm³/g pore volume and pore size centeredon 73 {acute over (Å)}. The aqueous solution containing sodium carbonatewas prepared by dissolving sodium carbonate in distilled H₂O. Thesorbent of Na₂O/γ-Al₂O₃ was prepared by an incipient wetness technique.As an example of sample preparation, 42.401 g of sodium carbonate wasdissolved in 100 g of distilled water. The total solution volume ofNa₂CO₃/H₂O adjusted with distilled water was 133 ml. 200 g of γ-Al₂O₃extrudates were impregnated with the solution by incipient wetness. Thesample was dried in air at 250° F. for 16 hours and calcined in air at1000° F. for 6 hours. The furnace was ramped at rate of 5° F./min.During the calcinations, the air flow was adjusted at 5 volume/volumesolid/minute. The sorbent contains 11.03 wt % expressed as Na₂O loading.

A series of samples containing different sodium loadings were alsoprepared similarly on γ-Al₂O₃ extrudates. The sodium contents in thesorbents as Na₂O are 3.01, 5.80, and 15.68 wt %, respectively.

Example 6 Sorbent Preparations

Additional samples of Na-based sorbents were prepared, including:

-   -   Theta-Al₂O₃ extrudates were used to deposit Na₂CO₃. It has        surface area of 126 m²/g, 0.58 cm³/g pore volume and pore size        of 143 {acute over (Å)}. The sorbent contains 11.03 wt % Na₂O as        loading.    -   Alpha-Al₂O₃ extrudates were used to deposit Na₂CO₃. It has        surface area of 0.8 m²/g, 0.46 cm³/g pore volume and pore size        of 2.8 micron. The sorbent contains 5.80 wt % Na₂O as loading.    -   Alpha- and Theta-mixture phase Al₂O₃ extrudates were used to        deposit Na₂CO₃. It has surface area of 32 m²/g, 0.15 cm³/g pore        volume and pore size of 155 {acute over (Å)}. The sorbent        contains 5.80 wt % Na₂O as loading.    -   SiO₂ extrudates were also used to deposit Na₂CO₃. It has surface        area of 178 m²/g, 0.86 cm³/g pore volume and pore size of 202        {acute over (Å)}. The sorbent contains 11.03 wt % Na₂O as        loading.

Example 7 Sorbent Preparation

The solution containing potassium nitrate was prepared by dissolvingpotassium nitrate in distilled H₂O. As an example of sample preparation,80.867 g of potassium nitrate was dissolved in 100 g of distilled water.The total solution volume of KNO₃/H₂O was adjusted with distilled waterto 133 ml. 200 g of gamma alumina extrudates were impregnated with thesolution by incipient wetness. The sample was dried in air at 250° F.for 16 hrs and calcined in air at 1000° F. for 6 hrs. The sorbentcontains 15.85 wt % K₂O

Other samples containing different potassium loadings were alsoprepared. The potassium contents in these sorbents expressed as K₂O are4.50 and 8.60 wt %, respectively.

Example 8 Simulated Moving Bed

An example using eight contactors with three on combustion gas, four onsteam, and one in purge is described below.

A bench-scale apparatus for demonstration of the process can be madefrom eight stainless steel beds. Each bed is made from a tubularenclosure with 3″ outer diameter with 0.065″ wall thickness by 4.5″long. Each bed holds 600 cc of the sorbent. Tests are run at near 1 atmpressure. The temperature range is 120 to 180° C. and the beds can berun so that they are maintained at near isothermal condition. Forexample the temperature of the beds can be between 150 and 165° C.during a full cycle including adsorption, regeneration and optionalpurge. The entire apparatus is maintained in a heated and insulated boxat near isothermal conditions. Individual beds are not heated or cooledduring cycling (e.g. not heated during regeneration, cooled duringadsorption, etc). The gas hourly space velocity (GHSV) in thisbench-scale apparatus is typically between 1000 to 3000 hr⁻¹ and inregeneration it is typically between 400 and 1000 hr⁻¹. Multiple 3-waycontrol values are used to control how each bed cycles through theadsorption, regeneration and an optional purge cycle. Typical cycletimes are 30 seconds to 150 seconds after which the gas flow switches tothe next cycle step. The cycle times can be adjusted to achievedifferent capture rates.

A non-limiting example of a bed configuration is shown in FIG. 22. Inthis example, 3 beds operate in adsorption, 4 beds in regeneration andone bed as a purge bed. The purge step displaces one bed volume ofregeneration gas back into the regeneration line and prevents CO₂ fromthe regeneration gas from being carried into flue outlet. The purge gasis then pushed back into the adsorber exhaust in the next cycle. Dry N₂is used as the purge gas. With 3 beds running in adsorption, eachindividual bed (whether in series or parallel operates in adsorptionmode for a total time of 3 times cycle time. With 4 beds inregeneration, each individual bed spends a total time of 4 times cycletime in regeneration.

In this example, the gases flow through the adsorption and regenerationbeds in series. With the beds in series, the flue gas travels throughall three adsorber beds before exiting the system. Likewise whenregeneration beds are configured in series, the regeneration steamsflows through all the regeneration beds before existing the system.

Other examples of bed configurations that can be utilized fordemonstration of this process in an 8 bed apparatus include but are notlimited to 3 beds in adsorption and 5 beds in regeneration; 2 beds inadsorption, 4 beds in regeneration and 2 beds in purge (betweenregeneration & adsorption and between adsorption and regenerationcycles); and 2 beds in adsorption, 5 beds in regeneration and 1 bed inpurge. The simulated flue gas can run through the beds in either seriesor parallel. The regeneration beds can also be configured in eitherseries or parallel. It is preferred to run the regeneration beds inseries.

Another example of the process operated in an 8 bed test apparatus withthe configuration shown in FIG. 22 included a simulated coal flue gas isshown FIG. 23, for the feed stream and adsorber outlet, and ademonstrated recovery stream in FIG. 24 (Percent CO₂ (in steam) inregeneration outlet in multiple fixed bed apparatus for near 90% Capturecase.) The simulated coal flue feed gas was 13.1% CO₂, 6% H₂O with thebalance N₂. The process was operated at near 1 atm with GHSV inadsorption of 1040 hr⁻¹ and GHSV in regeneration of 550 hr⁻¹. The bedstemperature was about 165° C. With a process cycle time of 110 s, theCO₂ loading was 0.88 wt % and 89.3% of the CO₂ was captured. The sorbentreduced the CO₂ concentration in the flue gas from 13% to 1.2%. Theoutlet CO₂ concentration in the regenerator is concentrated to 35% (withthe balance steam (any N₂ present was not measured). Sorbent wasprepared according to sorbent preparation Example 2.

In another example of the process operated in an 8 bed test apparatuswith the configuration shown in FIG. 22, the adsorber data is shown inFIG. 25. The simulated coal flue gas was 13.0% CO₂ and 4.2% H₂O with thebalance N₂. The process was operated at near 1 atm with GHSV inadsorption of 1410 hr⁻¹ and GHSV in regeneration of 420 hr⁻¹. The bedstemperature was about 175° C. Under these conditions we are starving theprocess of steam during regeneration. The cycle rate was 80 s. The CO₂in the outlet of regeneration is increasingly concentrated (>80% CO₂ insteam). The capture rate was 70% and the CO₂ dynamic loading 0.72 wt %CO₂, Sorbent was prepared according to sorbent preparation Example 2.

Example 9 Cyclic Adsorption/Steam Displacement

Samples were tested in the form of extrudate pellets, generally 1/16″ to⅛″ in diameter held in a cylindrical stainless steel vessel,approximately 1″×7.5″ and heated with a band heater, generally in therange of 130-150° C. The loaded bed typically holds 30 to 60 grams ofextrudates dependent on the bulk density of the adsorbents.

CO₂ containing feed is passed through the bed for adsorption at a flowrate of 1000 standard cubic centimeters per minute (sccm). Steam flowsare generated by flowing 0.3 cubic centimeters per minute of waterthrough a length of heated 1/16″ tubing, resulting in a steam flow rateof approximately 374 sccm.

CO₂ containing feed composition was 4% CO₂, 1% He, 8% H₂O, 8% O₂, and79% nitrogen.

While bed temperatures rise and fall in accordance with net adsorptionenergies, both feed and steam are heated to approximately 140° C. toenable and overall isothermal cyclic process.

The cyclic experiment comprises passing CO₂ containing feed through theadsorbent extrudates bed until full breakthrough of the feed compositionis determined, i.e. CO₂ concentration exiting the bed rises to its 4%concentration in the feed.

The adsorbent's capacity to adsorb CO₂ under the tested conditions isdetermined from the time from feed initiation the time when the CO₂concentration rises to half the feed concentration. On the assumption ofa symmetrical breakthrough front, this method closely approximates theamount of CO₂ that will be adsorbed when the bed is fully loaded. Theabove described time of adsorption is converted to a wt. % CO₂ capacityby multiplying by the CO₂ feed concentration and flow rate and dividingby the weight of adsorbent in the bed.

In the cyclic process, water is desorbed from the adsorbent as CO₂ isadsorbed. It is always observed that the bed temperature, as determinedby the temperature of the gases exiting the bed, drops during CO₂uptake. This “desorptive displacement phenomena” is in sharp contrast tosimple single gas adsorption, where the energy released by adsorptioncauses the bed temperature to rise.

Following the full feed breakthrough described above, CO₂ containingfeed is turned off and steam is introduced into the bed. As water isadsorbed on the bed and CO₂ is displaced, initially the void gases(non-adsorbed gases in the void volume within and without theextrudates) exit the reactor. Next, a high concentration “wave” ofrelatively dry CO₂ exits the bed. This “wave” has CO₂concentrations >50% and often >75-80%, diluted typically by nitrogen andwater vapor. The fact that CO₂ exits the bed at a concentration higherthan that in the feed distinguishes this desorptive displacement processfrom more typical purge, or partial pressure desorption processes.Following the high concentration CO₂ wave, steam breaks through the bed,having completed its adsorption. It is always observed that upon thesteam breakthrough that indicates that the water adsorption front hasproceeded to the end of the bed, the temperature rises. This phenomenaarises due to the greater heat of adsorption released by water'sadsorption as compared to the heat of desorption required for the CO₂'srelease.

The adsorbent's water capacity is determined from the time from steamintroduction to the time following the “CO₂ wave” whereupon highconcentration steam breaks through the bed.

The graphical data in FIG. 26 was typical for the experimental resultsand indicated the critical adsorption periods for this cyclicdisplacement process. This particular graphical representation was takenwithin a cyclic run of Sorbent A, discussed below.

Example 10 Effect of Water in the CO₂ Containing Feed

The properties of one formulation of sorbent are shown below. Thissorbent was fabricated by extrusion, which provides a relatively highcrush strength. The sorbent is very porous and has a moderately highsurface area. Although the theoretical loading is high (9%), the dynamicloading under the expected operating conditions is relatively low (0.4%to 1.0 wt %). This sorbent was employed in a number ofadsorption/regeneration cycles using simulated combustion gas (13.8%CO2) with varying water concentrations. The results, illustrated below,show that at 9% water the working capacity is reduced to 92% of that forzero water and that doubling the water concentration to 18% only reducesthe working capacity to 85% of the zero water value. The loading valuesin FIG. 27 are normalized by the zero water loading for eachtemperature.

A sample of sorbent prepared according to Sorbent Preparation Example 4was employed in a series of adsorption/regeneration cycles usingsimulated combustion gases containing 6% CO₂ by volume, and having waterconcentrations ranging from zero to 28.5 vol %. The results, illustratedin FIG. 28, show that even at the very high concentration of water theworking capacity for CO₂ was still more than half the capacity obtainedat zero water.

Example 11 Preparation and Testing of Sorbents A-I

Sorbent A: 13.5 wt. % K on Gamma Alumina Extrudates: γ-Al₂O₃ extrudateswere used as support to deposit K₂CO₃. It has a surface area of 306m²/g, pore volume of 0.85 cm³/g, and pore size centered on 73 {acuteover (Å)}. The solution containing potassium carbonate was prepared bydissolving potassium carbonate in distilled H₂O. As an example of thesample preparation, 27.6353 g of potassium carbonate was dissolved in 60g of distilled water. The total solution volume of K₂CO₃ was adjustedwith distilled water to 86 ml. 100 g of gamma alumina extrudates wereimpregnated with the potassium carbonate solution by incipient wetness.The sample was dried in air at 250° F. for 16 hrs. The K loading isdefined as weight of K/(weight of K+weight of alumina).

Sorbent B: 13.5 wt. % K on Theta Alumina Extrudates: θ-Al₂O₃ extrudateswere used to deposit potassium citrate. It has surface area of 126 m²/g,pore volume of 0.58 cm³/g, and pore size of 143 {acute over (Å)}. Thesolution containing potassium citrate was prepared by dissolvingpotassium citrate tribasic monohydrate (C₆H₅K₃O₇.H₂O) in distilled H₂O.As an example of the sample preparation, 64.866 g of potassium citratetribasic monohydrate was dissolved in 100 g of distilled water. Thetotal solution volume of potassium citrate was adjusted with distilledwater to 92 ml. 150 g of theta alumina extrudates were impregnated withthe potassium citrate solution by incipient wetness. The sample wasdried in air at 250° F. for 16 hrs. The sample was then placed in a boxfurnace which was purged with nitrogen flow for 1 hr before 53calcinations. The furnace was ramped at rate of 10° F./min from roomtemperature to 1000° F. (538° C.) under nitrogen flow and stayed at1000° F. (538° C.) under nitrogen for 3 hrs. The furnace was cooled downin nitrogen flow to room temperature. The nitrogen flow duringcalcinations steps was adjusted at 5 volume/volume solid/minute.

Sorbent C: 7.2 wt. % K on Theta Alumina Extrudates: The same θ-Al₂O₃extrudates as in the Example B were used for deposition of potassiumcitrate. The solution containing potassium citrate was prepared bydissolving potassium citrate tribasic monohydrate (C₆H₅K₃O₇.H₂O) indistilled H₂O. As an example of the sample preparation, 32.4035 g ofpotassium citrate tribasic monohydrate was dissolved in 100 g ofdistilled water. The total solution volume of potassium citrate wasadjusted with distilled water to 92 ml. 150 g of theta aluminaextrudates were impregnated with the potassium citrate solution byincipient wetness. The sample was dried in air at 250° F. for 16 hrs.The sample was then placed in a box furnace which was ramped at rate of10° F./min from room temperature to 1000° F. (538° C.) in air flow andstayed at 1000° F. (538° C.) in air for 3 hrs. The air flow duringcalcinations was adjusted at 5 volume/volume solid/minute.

Sorbent D: Sorbent D is equivalent to the sorbent preparation of Example2 above.

Sorbent E: 7.2 wt. % K on Carbon Extrudates: Carbon extrudates were usedto deposit potassium hydroxide. It has surface area of 1491 m²/g, porevolume of 0.73 cm³/g, and pore size of 46 {acute over (Å)}. The solutioncontaining potassium hydroxide was prepared by dissolving potassiumhydroxide in distilled H₂O. As an example of the sample preparation,5.6046 g of potassium hydroxide (KOH) was dissolved in 30 g of distilledwater. The total solution volume of potassium citrate was adjusted withdistilled water to 42 ml. 50 g of carbon extrudates were impregnatedwith the potassium hydroxide solution by incipient wetness. The samplewas dried in air at 250° F. for 16 hrs.

Sorbent F: 7.2 wt. % K on Theta Alumina Extrudates: The same θ-Al₂O₃extrudates as in the Example B were used for deposition of potassiumcarbonate. The solution containing potassium carbonate was prepared bydissolving potassium carbonate in distilled H2O. As an example of thesample preparation, 13.805 g of potassium carbonate (K₂CO₃) wasdissolved in 40 g of distilled water. The total solution volume of K₂CO₃was adjusted with distilled water to 62 ml. 100 g of theta aluminaextrudates were impregnated with the solution by incipient wetness. Thesample was dried in air at 250° F. for 16 hrs.

Sorbent G: 13.5 wt. % K on Gamma Alumina Extrudates: The same γ-Al₂O₃extrudates as in the Example A were used for deposition of potassiumcitrate. The solution containing potassium citrate was prepared bydissolving potassium citrate tribasic monohydrate (C₆H₅K₃O₇.H₂O) indistilled H₂O. As an example of the sample preparation 86.488 g ofpotassium citrate tribasic monohydrate was dissolved in 120 g ofdistilled water. The total solution volume of potassium citrate wasadjusted with distilled water to 173 ml. 200 g of gamma aluminaextrudates were impregnated with the potassium citrate solution byincipient wetness. The sample was dried in air at 250° F. for 16 hrs.The sample was then placed in a box furnace which was ramped at rate of10° F./min from room temperature to 1000° F. (538° C.) in air flow andstayed at 1000° F. (538° C.) in air for 3 hrs. The air flow duringcalcinations was adjusted at 5 volume/volume solid/minute.

Sorbent H: 7.2 wt. % K on Theta Alumina Extrudates: The same θ-Al₂O₃extrudates as in the Example B were used for deposition of potassiumcitrate. The solution containing potassium citrate was prepared bydissolving potassium citrate tribasic monohydrate (C₆H₅K₃O₇.H₂O) indistilled H₂O. As an example of the sample preparation, 64.807 g ofpotassium citrate tribasic monohydrate was dissolved in 180 g ofdistilled water. The total solution volume of potassium citrate wasadjusted with distilled water to 185 ml. 300 g of theta aluminaextrudates were impregnated with the potassium citrate solution byincipient wetness. The sample was dried in air at 250° F. for 16 hrs.The sample was then placed in a box furnace which was ramped at rate of10° F./min from room temperature to 1000° F. (538° C.) in air flow andstayed at 1000° F. (538° C.) in air for 3 hrs. The air flow duringcalcinations was adjusted at 5 volume/volume solid/minute.

Sorbent I: 12.1 wt. % Na on Gamma Alumina Extrudates: The same γ-Al₂O₃extrudates as in the Example A were used for deposition of sodiumcarbonate. The solution containing sodium carbonate was prepared bydissolving sodium carbonate in distilled H₂O. As an example of samplepreparation, 15.90 g of sodium carbonate was dissolved in 25 g ofdistilled water. The total solution volume of Na₂CO₃ was adjusted withdistilled water to 43 ml. 50 g of gamma alumina extrudates wereimpregnated with the sodium carbonate solution by incipient wetness. Thesample was dried in air at 250° F. for 16 hrs. The sample was thenplaced in a box furnace which was ramped at rate of 10° F./min from roomtemperature to 1000° F. (538° C.) in air flow and stayed at 1000° F.(538° C.) in air for 3 hrs. The air flow during calcinations wasadjusted at 5 volume/volume solid/minute.

Cyclic Adsorption Capacity Determinations for Sorbents A through I

The following Table shows the measured adsorbent capacities for CO₂,H₂O, and the CO₂ ratio for a number of non-limiting adsorbentpreparations. We have found that various supports for the alkali metalscan all be effective. Further, we have found that addition of the alkalito a formed extrudates or pellet or can be added to the base supportmaterial and later formed into the desired sphere, extrudates, or pelletform can be done by most methods known to those skilled in the art.Below, we demonstrate adsorbents composed of either potassium or sodium,added as either carbonates or bicarbonates, hydroxides, or asorganometallic species (the non-limiting example of potassium citrate isshown that is then calcined or pyrolyzed).

Table of Cyclic Displacement Adsorbent Capacities H₂O/CO₂ % CO₂ % H₂OMole Ratio Added As Sorbent A 13.5 wt. % K on Gamma Alumina 1.09 1.984.4 Potassium Extrudates Carbonate Sorbent B 13.5 wt. % K on ThetaAlumina 0.85 1.08 3.1 Potassium citrate— Extrudates pyrolyzed in N2Sorbent C 7.2 wt. % K on Theta Alumina 0.78 1.87 5.9 PotassiumExtrudates Citrate— calcined Sorbent D 9 wt. % Na extruded on Boehmite0.76 2.1 6.8 Sodium and Calcined Bicarbonate Sorbent E 7.2 wt. % K onCarbon Spheres 0.77 2.72 8.6 KDH Sorbent F 7.2 wt. % K on Theta Alumina0.53 1.73 8.0 Potassium Extrudates Carbonate Sorbent G 13.5 wt. % K onGamma Alumina 1.48 3.5 5.8 Potassium Extrudates Citrate— calcinedSorbent H 7.2 wt. % K on Theta Alumina 0.68 7.73 6.2 PotassiumExtrudates Citrate— calcined Sorbent I 12.1 wt. % Na on Gamma 1.04 2.796.6 Sodium Alumina Extrudates Carbonate

Note that Sorbent E was tested without the presence of air as it wasobserved that carbon gasification was taking place. It is suggested thatcarbon supported adsorbents useful in this process are best used inanaerobic conditions such as those found in natural gas CO₂ removalprocesses.

Example 12 CO₂ Loading Capacities

Alkalized sorbents for the disclosure can be assessed for CO₂ loadingcapacities. Isothermal testing was conducted to measure the ultimateloading capacities of different sets of alkalized supports. Tests wereconducted across several % wt alkali compositions, and the results ofshown in FIGS. 29A and 29B.

Example 13 8 Bed Simulated Moving Bed System with Adsorption Run inParallel

An 8-bed simulated moving bed system was constructed in which theadsorption zone of the system included beds run in parallel rather thanin series. An exemplary diagram is shown in FIG. 30. The bench scaleapparatus was run as previously described, monitoring the CO₂ in fluegas feed, the breakthrough of CO₂ at the adsorbers outlet, and the CO₂at the regeneration outlet. Beds were operated in a 2:6, 3:5, and 4:4adsorber:regeneration sequence. Results are set forth in the Table 5,with figures for the CO₂ levels shown in FIGS. 31-33, as noted in thetable.

Adsorb:Regen Loading levels Capture Associated Bed Ratio of CO₂percentage FIGS. 2:6 0.82 wt % 88.3% FIG. 31 3:5 0.83 wt % 90.3% FIG. 324:4 0.83% 88.7% FIG. 33

Example 14 10 Bed Simulated Moving Bed System with Optional RecycleStreams

A 10-bed simulated moving bed system was constructed in which theadsorption zone of the system included beds run in parallel rather thanin series. An exemplary diagram is shown in FIG. 34A to 34D.

Example 15 10 Bed Simulated Moving Bed System with Optional Steam Saver

A 10-bed simulated moving bed system can be constructed thatdemonstrates a steam saver method at a commercial level, as shown inFIGS. 35A-35D. The method can address unsteady flows and segregate thesteam saver effluent from the regen effluent. The flue gas can be splitacross 4 beds, in parallel, with the bed just coming on adsorptiongetting 1/7 of the total flow, and the other three getting 2/7 each. Theeffluent from the first bed on adsorption can be directed to the bedthat just left adsorption and the effluent from that bed can go to vent(recycle), leading to approximately 14% of the flue gas being divertedto steam saving, and equivalent to diverting one of three beds for 43%of a cycle (38 seconds out of 90). The method can eliminate mixing steamsaver gas with regen gas, and reduce need for a means to accommodateuneven flows during steam saver steps, such as via surge vessels. Thereduced rate of flow during steam saving can reduce pressure drop sothat the flue gas can flow through the two beds (one generating steamsaving gas and the other re-adsorbing the saved steam) in series withthe same or a little bit less pressure drop than the beds feeding the2/7 of the flue gas each, eliminating the need for a possible no steamsaver blower.

EMBODIMENTS

Additionally or alternately, the disclosure can include one or more ofthe following embodiments.

Embodiment 1. A process for separating CO₂ from a gas stream, comprisingpassing a gas streaming comprising CO₂ over a sorbent to adsorb the CO₂to the sorbent, recovering the CO₂ by desorbing the CO₂ from thesorbent, wherein the process does not include pressure swing adsorptionand temperature swing adsorption.

Embodiment 2. A sorbent based CO₂ adsorption process, comprising thesteps of preparing a sorbent comprising an alkalized substrate, passinga gas stream containing CO₂ across the sorbent to adsorb the CO₂ ontothe alkalized substrate, recovering the CO₂ from the sorbent by passingsteam across the CO₂ containing alkalized substrate to displace the CO₂with water.

Embodiment 3. A CO₂ separation system comprising a CO₂ adsorption zone;a CO₂ desorption zone; one or more CO₂ sorbent beds, and a CO₂ feedstream; wherein the sorbent bed alternates between the adsorption zoneand the desorption zone; adsorbs CO₂ from the CO₂ feed stream in theadsorption zone and desorbs CO₂ in the desorption zone; and does notinclude a pressure swing or a temperature swing adsorption.

Embodiment 4. A method for purifying a CO₂ gas stream to increase theconcentration of the CO₂ in a product stream, comprising the steps ofpreparing a sorbent bed having an inlet and an outlet passing a gasstream containing CO₂ across the sorbent bed to adsorb the CO₂ to thesorbent recovering a CO₂-enriched stream by passing steam across the CO₂containing sorbent, wherein the method does not include a pressure swingadsorption or temperature swing adsorption process.

Embodiment 5. A method for removing CO₂ to purify a gas stream,comprising the steps of a) preparing a sorbent bed having an inlet andan outlet passing a gas stream containing CO₂ across the sorbent bedfrom inlet to outlet to adsorb the CO₂ to the sorbent, recovering thepurified gas stream depleted of CO₂ at the outlet, and regenerating thesorbent bed by passing steam across the CO₂ containing sorbent, whereinthe method does not include a pressure swing adsorption or temperatureswing adsorption process.

Embodiment 6. The methods, processes, or systems of one of the previousembodiments, wherein the adsorption of CO₂ occurs by concentration swingadsorption and adsorptive displacement

Embodiment 7. The methods, processes, or systems of one of the previousembodiments, wherein the process, method or system does not includepressure swing adsorption or temperature swing adsorption.

Embodiment 8. The methods, processes, or systems of one of the previousembodiments, wherein the desorption of CO₂ from the sorbent duringrecovery or regeneration is by a combination of concentration swingdesorption and desorptive displacement.

Embodiment 9. The methods, processes, or systems of one of the previousembodiments, wherein the desorption or recovery of the CO₂ includestreating the sorbent with steam to displace the CO₂ from the sorbent.

Embodiment 10. The methods, processes, or systems of one of the previousembodiments, the steps are conducted at a constant pressure.

Embodiment 11. The methods, processes, or systems of one of the previousembodiments, wherein the steps are conducted at approximately isothermalconditions.

Embodiment 12. The methods, processes, or systems of one of the previousembodiments, wherein the temperature decreases during adsorption by nomore than about 30° C., or 25° C., or 20° C., or 15° C., or 10° C.

Embodiment 13. The methods, processes, or systems of one of the previousembodiments, wherein the temperature increases during desorption orregeneration by no more than about 30° C., or 25° C., or 20° C., or 15°C., or 10° C.

Embodiment 14. The methods, processes, or systems of one of the previousembodiments, wherein the amount of CO₂ in the feed stream has beenreduced by at least about 80% by volume, or 85% by volume, or 90% byvolume.

Embodiment 15. The methods, processes, or systems of one of the previousembodiments, wherein greater than 80% by volume, or 85% by volume, or90% by volume of the CO₂ has been recovered in the CO₂-enriched streamof the regenerated or desorbed sorbent

Embodiment 16. The methods, processes, or systems of one of the previousembodiments, wherein the sorbent bed includes a sorbent.

Embodiment 17. The methods, processes, or systems of one of the previousembodiments, wherein the sorbent is an alkalized substrate, or analkalized alumina.

Embodiment 18. The methods, processes, or systems of one of the previousembodiments, wherein the alkalized substrate comprises an aluminacomponent and at least one alkali or alkaline earth component.

Embodiment 19. The methods, processes, or systems of one of the previousembodiments, wherein the alkalized substrate consists essentially of analumina component and at least one alkali or alkaline earth component.

Embodiment 20. The methods, processes, or systems of one of the previousembodiments, including an inlet and an outlet for the adsorption zone oradsorption bed where the CO₂ feed stream enters the adsorption zone orbed via the inlet and a purified feed stream exits the adsorption zoneor bed via the outlet. stage, wherein a stream comprising steam entersthe desorption zone via the inlet and a CO₂ enriched stream exits viathe outlet

Embodiment 21. The methods, processes, or systems of one of the previousembodiments, including an inlet and an outlet for the desorption zonewhere the stream comprising steam enters the desorption zone via theinlet and a CO₂ enriched stream exits the desorption zone via theoutlet.

It is to be understood that the embodiments and claims disclosed hereinare not limited in their application to the details of construction andarrangement of the components set forth in the description andillustrated in the drawings. Rather, the description and the drawingsprovide examples of the embodiments envisioned. The embodiments andclaims disclosed herein are further capable of other embodiments and ofbeing practiced and carried out in various ways. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting theclaims.

Accordingly, those skilled in the art will appreciate that theconception upon which the application and claims are based can bereadily utilized as a basis for the design of other structures, methods,and systems for carrying out the several purposes of the embodiments andclaims presented in this application. It is important, therefore, thatthe claims be regarded as including such equivalent constructions.

We claim:
 1. A process for separating CO₂ from a gas stream, comprisinga) passing a gas stream comprising CO₂ over a sorbent to adsorb the CO₂to the sorbent, b) recovering the CO₂ by desorbing the CO₂ from thesorbent, wherein the process does not include pressure swing adsorptionor temperature swing adsorption, wherein step b) includes desorption ofthe CO₂ from the sorbent by a combination of concentration swingdesorption and desorptive displacement, the concentration swingdesorption comprising partial pressure purge desorption and thedesorptive displacement comprising a process wherein an adsorbed CO₂molecule is displaced from the sorbent by steam during the desorptionstep.
 2. The process of claim 1, wherein step a) includes adsorption ofCO₂ by concentration swing adsorption and adsorptive displacement. 3.The process of claim 1, wherein steps a) and b) are conducted at aconstant pressure.
 4. The process of claim 1, wherein steps a) and b)are conducted at approximately isothermal conditions.
 5. The process ofclaim 1, wherein the temperature of the sorbent decreases during step a)by no more than about 20° C.
 6. The process of claim 1, wherein thetemperature of the sorbent increases during step b) by no more thanabout 20° C.
 7. The process of claim 1, wherein the sorbent comprises analkalized substrate.
 8. The process of claim 1, wherein the sorbentcomprises an alkalized alumina.
 9. A sorbent based CO₂ adsorptionprocess, comprising the steps of a) preparing a sorbent comprising analkalized substrate, b) passing a gas stream containing CO₂ across thesorbent to adsorb the CO₂ onto the alkalized substrate, c) recoveringthe CO₂ from the sorbent by passing steam across the alkalized substrateto displace the carbon dioxide adsorbed on the alkalized substrate withwater.
 10. The process of claim 9, wherein the process does not includepressure swing adsorption or temperature swing adsorption.
 11. Theprocess of claim 9, wherein step b) comprises adsorption of CO₂ byconcentration swing adsorption and adsorptive displacement.
 12. Theprocess of claim 9, wherein step c) comprises recovering the CO₂ by acombination of concentration swing desorption and desorptivedisplacement.
 13. The process of claim 9, wherein the alkalizedsubstrate comprises a substrate and at least one alkali or alkalineearth component.
 14. The process of claim 9, wherein the alkalizedsubstrate comprises an alumina component and at least one alkali oralkaline earth component.
 15. The process of claim 9, wherein thealkalized substrate consists essentially of an alumina component and atleast one alkali or alkaline earth component.
 16. The process of claim9, wherein the temperature of the sorbent decreases during step b) by nomore than about 20° C.
 17. The process of claim 9, wherein thetemperature of the sorbent increases during step c) by no more thanabout 20° C.
 18. A CO₂ separation system, comprising: a CO₂ feed stream;a CO₂ adsorption zone; a CO₂ desorption zone; one or more CO₂ sorbentbeds, wherein the one or more sorbent beds alternates between the CO₂adsorption zone and the CO₂ desorption zone, and wherein the one or moresorbent beds adsorbs CO₂ from the CO₂ feed stream in the adsorption zoneand desorbs CO₂ in the desorption zone; wherein the CO₂ separationsystem does not include a pressure swing or a temperature swingadsorption, and wherein the desorption zone operates as a concentrationswing and a desorptive displacement, the concentration swing comprisingpartial pressure purge desorption and the desorptive displacementcomprising a process wherein an adsorbed CO₂ molecule is displaced fromthe sorbent by steam during the desorption step.
 19. The system of claim18, further comprising an inlet and an outlet for the adsorption zonewhere the CO₂ feed stream enters the adsorption zone via the inlet and apurified gas stream exits the adsorption zone via the outlet.
 20. Thesystem of claim 18, further comprising an inlet and an outlet for thedesorption zone, wherein a stream comprising steam enters the desorptionzone via the inlet and a CO₂ enriched stream exits via the outlet. 21.The system of claim 18, further comprising a purge zone after thedesorption zone, wherein the one or more sorbent beds enters the purgestage and is purged via a stripping gas stream.
 22. The system of claim18, wherein the one or more sorbent beds comprises a sorbent, and thesorbent comprises a substrate and at least one alkali or alkaline earthcomponent.
 23. The system of claim 18, wherein the one or more sorbentbeds comprises a sorbent, and the sorbent comprises an alumina componentand at least one alkali or alkaline earth component.
 24. The system ofclaim 18, wherein the adsorption zone operates as a concentration swingand adsorptive displacement.
 25. The system of claim 18, wherein theadsorption zone has an adsorption inlet and an adsorption outlet, thedesorption zone has a desorption inlet and a desorption outlet, and theadsorption inlet and adsorption outlet are in opposing positions fromthe desorption inlet and the desorption outlet, relative to the one ormore sorbent beds.
 26. The system of claim 18, wherein the one or moresorbent beds comprises at least two sorbent beds, and the at least twosorbent beds rotate through each of the adsorption and desorption zones.27. The system of claim 18, wherein the one or more sorbent bedscomprises a plurality of sorbent beds rotating in series through theadsorption zone, desorption zone, and optionally though a purge stageafter the desorption zone.
 28. A method for purifying a CO₂ gas streamto increase the concentration of the CO₂ in a product stream, comprisingthe steps of a) preparing a sorbent bed having an inlet and an outlet,b) passing a gas stream containing CO₂ across the sorbent bed to adsorbthe CO₂ to the sorbent, and c) recovering a CO₂-enriched stream bypassing steam across the CO₂ containing sorbent, wherein the method doesnot include a pressure swing adsorption or temperature swing adsorptionprocess, and wherein the CO₂ is recovered by a combination ofconcentration swing desorption and desorptive displacement, theconcentration swing desorption comprising partial pressure purgedesorption and the desorptive displacement comprising a process whereinan adsorbed CO₂ molecule is displaced from the sorbent by steam duringthe desorption step.
 29. The method of claim 28, wherein the CO₂ isadsorbed in step b) by a concentration swing adsorption and adsorptivedisplacement.
 30. The method of claim 28, wherein greater than 80% byvolume of the CO₂ has been recovered in the CO₂-enriched stream.
 31. Themethod of claim 28, wherein greater than 85% by volume of the CO₂ hasbeen recovered in the CO₂-enriched stream.
 32. The method of claim 28,wherein greater than 90% by volume of the CO₂ has been recovered in theCO₂-enriched stream.
 33. A method for removing CO₂ to purify a gasstream, comprising the steps of a) preparing a sorbent bed having aninlet and an outlet, b) passing a gas stream containing CO₂ across thesorbent bed from inlet to outlet to adsorb the CO₂ to the sorbent, c)recovering the purified gas stream depleted of CO₂ at the outlet, and d)regenerating the sorbent bed by passing steam across the CO₂ containingsorbent, wherein the method does not include a pressure swing adsorptionor temperature swing adsorption process, and wherein the sorbent bed isregenerated by a combination of concentration swing desorption anddesorptive displacement, the concentration swing desorption comprisingpartial pressure purge desorption and the desorptive displacementcomprising a process wherein an adsorbed CO₂ molecule is displaced fromthe sorbent by steam during the desorption step.
 34. The method of claim33, wherein the CO₂ is adsorbed in step b) by a concentration swingadsorption and adsorptive displacement.
 35. The method of claim 33,wherein the amount of CO₂ in the purified gas stream has been reduced byat least 80% by volume.
 36. The method of claim 33, wherein the amountof CO₂ in the purified gas stream has been reduced by at least 85% byvolume.
 37. The method of claim 33, wherein the amount of CO₂ in thepurified gas stream has been reduced by at least 90% by volume.